Known Space is the fictional setting of some dozen science fiction novels and several collections of short stories written by author Larry Niven. It has also in part been used as a shared universe in the Man-Kzin Wars spin-off anthologies sub-series.
The epithet "Known Space" is an in-universe term that refers to a relatively small part of the galaxy centered around Earth. In the future that the series depicts (beginning a few centuries from now and continuing for about a millennium afterward) this region has been explored by humans and a number of its worlds have been colonized. Contact has been made with alien species such as the two-headed Pierson's Puppeteers and the aggressive felinoid Kzinti. The fictional universe is also the home of species from outside Known Space, including the hominid inhabitants of a megastructure called Ringworld. The Ringworld orbits a sun outside Known Space, but it is a well-established artifact within the Known Space "universe". The stories span approximately one thousand years of future history, from the first human explorations of the Solar System to the colonization of dozens of nearby systems. Late in the series, this area is an irregularly shaped "bubble" about 60 light-years across.
The stories that constitute the Known Space series were originally conceived as two separate series: the Belter stories, featuring solar-system colonization and slower-than-light travel with fusion-powered and Bussard ramjet ships, and the Neutron Star/Ringworld series of stories, set much further into the future, which feature faster-than-light ships using "hyperdrive". The two timelines were implicitly joined by Niven in the story A Relic of the Empire, in which the background elements of the Slaver civilization (introduced in World of Ptavvs, from the Belter series) was used as a plot element of a story in the faster-than-light setting. Roughly 300 years separate the timeline of the last stories of the early setting (which are set roughly between 2000 and 2350), from the earliest stories in the later setting (set in 2651 (Neutron Star) and later). In the late 1980s, Niven opened up this gap in the known space timeline as a shared universe, and the stories of the Man-Kzin Wars volumes fill in that history, bridging the two settings.
In the process of exploring space, humankind encounters several intelligent alien species, including the following (in alphabetical order):
- Bandersnatchi: Colossal slug-like creatures, originally created by the Tnuctipun as a food source for the Thrintun. Believed by the Thrintun to be unintelligent, the Bandersnatchi (known to the Thrintun as Whitefoods) were engineered by the Tnuctipun to be highly intelligent spies for their war on the Thrintun. At one time found on every Thrint estate throughout the Thrintun empire, the only known survivors in Known Space are on the planet Jinx, though they are later found on the Ringworld and on a forested planet called Beanstalk (in the Man-Kzin Wars story "Hey Diddle Diddle"). The Bandersnatchi were the only intelligent species which were immune to the Thrint mental power.
- Chunquen: A slave species of the Kzinti, remarkable to their captors for the sentience of both sexes. ("They fought constantly.")  Their homeworld is watery; they resisted the Kzinti invasion with missiles fired from submarine ships. Apparently exterminated before the Kzinti first encountered humans.
- Grogs: Sessile sentient creatures, shaped like furry cones. They are eyeless, earless, and have a prehensile tongue. They can also control animals telepathically. The Grogs are thought by some to be the descendants of the Thrintun species, after 1.5 billion years of atrophy.
- Gw'oth: Starfish-shaped beings inhabiting the ice moon of a gas giant. GW'oth possess the ability to link their neural tissue and form incredibly powerful and efficient biological supercomputers, called Gw'otesht. GW'otesht typically exist in collections of individual Gw'oth in multiples of 4, the largest known comprising 16 entities. GW'otesht are capable of running many millions of complex simulations in a short amount of time, giving them the ability to plan ahead in great detail by analyzing every possible outcome. Evolving to sentience from colonies of carnivorous tubeworms living beneath the ocean of an ice moon similar to Europa, the Gw'oth broke through the ice and first experimented with fire only two generations previous to mastering nuclear fission. The Gw'oth continue to advance rapidly without need for trial and error learning. They know nothing of other intelligent beings in the universe until first encountering Humans and Pierson's Puppeteers in Fleet of Worlds. Though superficially similar to the Jotoki, they are unrelated.
- Jotoki: Sentient starfish-shaped beings formed by the joining of the lobes of five non-sentient eel-like life forms into a single brain. Former rulers of an interstellar empire, they used Kzinti as bodyguards and mercenaries, but the Kzinti took over the Jotoki empire and built their own upon it, making the Jotoki slaves and food animals. Though superficially similar to the Gw'oth, they are unrelated.
- Kdatlyno: A slave species of the Kzinti until humans freed them, although some are still legal Kzinti slaves. Kdatlyno are huge, 10-foot-tall (3.0 m) bipeds with long arms. They have a thick brown hide, curved claws at knees and elbows, and retractable claws on the knuckles of their hands. Their heads are eyeless and noseless, with a gash of a mouth. Above that is a goggle-shaped tympanum (eardrum), which allows them to "see" by way of sonar. Kdatlyno create 'touch sculptures' as an art form. Other species need to touch this art, rather than look at it, to appreciate it properly.
- Kzinti: Large and very aggressive felinoid aliens with whom humans fight several brutal interstellar wars. Kzinti tactics are somewhat cat-like in nature, "scream and leap" being the primary mode of declaring a challenge. The first Man-Kzin War ended when the humans obtained the faster-than-light drive (FTL) from the Outsiders, after which the Kzinti ships stood no chance against the FTL warships. Throughout the rest of the wars with man, the Kzinti tended to always attack before they were ready, and subsequently lost all of them. As a result of this most of their empire was lost; in the peace treaties that resulted, colonies and slave planets were ceded to man or given independence. In Ringworld it is revealed that this was in part due to clandestine meddling by the Pierson's Puppeteers. They saw in the aggressive Kzinti a major threat, and orchestrated the events that led to the humans getting FTL ships and thereby ensuring the human victory of the first war. Each of these Kzinti defeats eliminated the most aggressive individuals from the Kzinti gene pool and thus made the Kzinti more "manageable" from a Puppeteer point of view. By the time Ringworld takes place, Kzinti are able to deal with other races diplomatically, rather than by attacking and enslaving them. Female Kzinti are not sapient, although among the archaic Kzinti found on the Ringworld some are. The protagonist Louis Wu thinks this indicates the Kzinti in Known Space have bred intelligence out of their females.
- Niven himself wrote little about the Man-Kzin Wars, although many of his stories refer to them having taken place in the past. The Man-Kzin Wars short-story collections were primarily written by other authors. The Kzinti "crossed-over" into the Star Trek universe in the animated episode "The Slaver Weapon", which was written by Larry Niven and is adapted from Niven's own short story "The Soft Weapon".
- In the Man-Kzin Wars novel Destiny's Forge, it is revealed that the Black Priests, a powerful cult within the Patriarchy whose members all have completely black pelts, have been responsible for the breeding program to isolate the telepath gene and preserve kzinrret subsapience. Kits are tested while young; a female who displays too much intelligence is taken away and killed, and a male who displays knowledge they could not have gotten except by telepathy is taken away and addicted to sthondat lymph to become a Telepath. On Kzinhome, however, the czrav and forest nomad prides, outcasts from mainstream Kzinti culture, never accepted the Black Priests, and in consequence have fully sentient kzinrretti, although this fact is a carefully held secret.
- Martians: Primitive but intelligent humanoids who lived beneath the sands. Martians burst into flames when brought in contact with water. Martians killed many of the early human explorers on Mars, principally because they concealed their existence, and they weren't suspected. In the novel Protector, the Martians were wiped out when Jack Brennan caused an ice asteroid to crash into the surface of Mars, raising the average humidity of the atmosphere. Some Martians still exist on the "Map of Mars" on the Ringworld.
- Morlocks: Semi-sentient humanoid cave dwellers on Wunderland. They, like humans, descended from a failed attempt by Pak Protectors to colonize Sol and nearby star systems. Named by humans for the creatures in H.G. Wells' The Time Machine.
- Nonesuch: A carnivorous species with telepathic abilities, that they primarily use for hunting prey and, most probably, for communication. The only predator of planet Haven. Not fully described, due to the fact that it somehow clouds the mind of its prey (that once included the human settlers). But it is intellectually handicapped, in that in combination with its telepathy, automatically assumes loss of ego when presented with a powerful telepathic feedback (i.e. from a human): It can assume a catatonic, unconscious state if a human it has telepathically linked thinks that it's just imagined a Nonesuch: thus the name. (from "Convergent Series")
- Outsiders: very advanced, fragile aliens shaped like cats o' nine tails that, according to Ringworld, probably evolved on a cold, low gravity world resembling Nereid. They mostly live on big ships, crossing the interstellar space at sublight velocities (according to A Gift From Earth, they find hyperspace vulgar), trading in information and technology. They possess inertial dampers and planetary drives. It was the Outsiders that sold humans the FTL drive, on a stop in the solar system of the human colony called We Made It. The Outsider ships' paths between the stars are determined by the starseeds, which they for some unknown reason seem to follow. The starseeds are gigantic, non-sentient space-dwelling animals that travel from the galactic core to the rim by their solar sails. At the rim they lay their eggs, then travel the 50,000 light-years back to the core.
- Pak: Interstellar ancestors of humanity (actually Homo habilis) whose life-cycle mimics the stages of human aging. Pak live through three stages of being: Child, breeder, protector. A Pak breeder who reaches 30 to 45 years of age will feel an irresistible urge to eat the sweet-potato-like root of a plant, Tree-of-Life, that is found throughout the Pak homeworld. A virus found in tree-of-life initiates the transformation into a protector. Protectors lose all sense of gender and reproductive desire, and exist solely to defend their clan bloodline. They are xenophobic, violent, hyper-intelligent and driven only by the fierce instinct to protect their descendants. This powerful instinct drove them to commit genocide on several planets where they tried to establish colonies, since every other sentient species was considered a potential threat. It also led to relentless internecine wars whenever two familial lines wound up with goals in conflict. When the Protectors reappear in The Ringworld Engineers and its sequels, it is strongly indicated that they constructed the Ringworld. A Pak colony failed on Earth 2.5 million years ago due to the soil's lack of thallium, which allowed Tree-of-Life to flourish but not the virus within its roots. As a result several million Pak breeders spread across the Earth, eventually evolving into Homo sapiens sapiens and all other primate life on the planet. Likewise, every hominid species found on the Ringworld is descended from Pak breeders, and all are susceptible to the virus of Tree-of-life. A protector-stage Homo habilis is more intelligent than a breeder-stage Homo sapiens, and a protector stage Homo sapiens is even more intelligent.
- Pierin: A slave species of the Kzinti. At the time of their conquest, they occupied several planets near p Eridani. No description is given, but the Ringworld RPG suggests they resemble horned birds and that their homeworld has low gravity. Presumably freed by humans, but this is not attested.
- Pierson's Puppeteers: A technologically advanced race of three-legged, twin-necked herbivores descended from herd animals, and noted for their so-called cowardice. Their commercial empire directly and indirectly controls events throughout Known Space and beyond, and Puppeteer plots are behind many of the larger events in Known Space. The name "Puppeteer" is purportedly derived from the twin "heads" (not enclosing brains) which perform as both mouths and hands, which strongly resemble sock puppets. The Puppeteer voice range is far greater than the human one, but for speaking to humans they adopt the tone of a very seductive female. It is also suggested that the "Puppeteer" name may derive from their social tendency to be very manipulative. The species were depicted in Barlowe's Guide to Extraterrestrials
- Thrintun: An ancient species that ruled a large empire, including the region of Known Space, through telepathic mind control about 1.5 billion years ago. A technology created by one of their slave races was the stasis field, which makes its contents impervious to harm and provides indefinite suspended animation, which has figured in several Known Space stories. Thrintun were small (approximately 1.25 meters tall), highly telepathic but not particularly intelligent (with their mind control, they did not need to be), reptilian, with green scaly skin, pointed teeth, and a single eye. The species were depicted in Barlowe's Guide to Extraterrestrials
- Tnuctipun: An apparently extinct ancient race of small carnivores contemporaneous with and enslaved by the Thrintun. They were known for their technological prowess, especially in genetic engineering. They secretly planned and executed the revolution to overthrow their Thrintun masters using many of their creations. When it appeared that the revolt would succeed, the Thrintun elders built and used a psychic amplifier that forced every sentient being in the galaxy to commit suicide, the signal repeating for centuries. The Thrintun that survived the revolt died out when all their slave races were dead.
- Trinocs: Named for their three eyes; they also have three fingers on each hand and a triangular mouth. They are described as 5-foot-tall (1.5 m) bipedal humanoids, with long legs, short torsos, and improbably flexible neck vertebrae. An unconfirmed source states that they breathe a "primordial reducing atmosphere" mainly composed of methane and ammonia, and are culturally paranoid, at least by human standards. First encountered by Louis Wu in the short story "There is a Tide".
- Whrloo: Meter-tall insectoids with long eyestalks, their homeworld has low gravity with a thick, dense atmosphere. They never saw the stars until they were enslaved by the Kzinti.
Also figuring in some stories are dolphins and other intelligent cetaceans, and various offshoots of Homo sapiens including the associate lineage of the hominids of the Ringworld. Most life in Known Space shares similar biochemistries, since they evolved from the Thrintun practice of seeding barren worlds with food yeast which they used to feed their slaves. Over a billion years, the Thrintun food yeast evolved into the different life forms in Known Space.
One aspect of the Known Space universe is that most of the early human colonies are on planets suboptimal for Homo sapiens. During the first phase of human interstellar colonization (i.e. before humanity acquired FTL), simple robotic probes were sent to nearby stars to assess their planets for habitation. The programming of these probes was flawed: they sent back a "good for colonization" message if they found a habitable point, rather than a habitable planet. Sleeper ships containing human colonists were sent to the indicated star systems. Too often, those colonists had to make the best of a bad situation.
- Earth, the human homeworld, is oppressively ruled by the United Nations, which wields its power by means of the ARM, a global police force. For centuries, due to the perfection of organ transplant technology, all state executions were done in hospitals to provide organ transplants, and to maximize their availability nearly all crimes carried the death penalty, including such offenses as multiple traffic tickets or tax evasion. This period ended when Jack Brennan, who had consumed the Tree-of-Life root and become a human version of the Pak Protector, used his superior intelligence to engineer social change in medical technology and social attitudes that eventually reduced the use of organ banks to reasonable levels. Part of Brennan's manipulation was the development of a science known as "psychistry". Psychistry was used to "correct" all forms of "mental aberration" - the populace is extremely docile. To combat overpopulation (one estimate is 18 billion people), a license is required to procreate, only available after exhaustive testing has determined that a prospect is free of "abnormalities"; unlicensed procreation is a capital crime. This policy, in addition to the existence of the transfer booth and a one-world language and economy, has led to the populace eventually becoming fairly genetically homogeneous. To prevent the development of new WMDs, all scientific research is regulated by the government and potentially dangerous technology is suppressed. Due to such suppression, Earth has had fewer real breakthroughs in science than would be expected. A common title for people born on Earth is "Flatlander"; having been born and raised in the only environment in Known Space to which humans are well-adapted, they are considered naïve and a bit helpless by humans from colony worlds.
- The Moon is a separate entity, but is under the control of the same government as Earth. It, however, has its own distinct culture. Humans native to the Moon are called "Lunies", and tend toward tall, lean body types regularly reaching eight feet in height. They are frequently referred to as looking much like Tolkien's Elves due to their physiques and alien allure.
- Mars, fourth planet in our solar system and the first planetary colony in Known Space. Native "Martians" were exterminated by the Brennan Monster. No one goes there, as resources are easier to mine in the Belt and Jovian moons. Earth ultimately colonized Mars specifically to study the descent landing pod used by Phssthpok the Pak in 2124 AD and was still in existence in 2183 when the Martians were exterminated by Brennan. The colony expanded greatly during the first Man-Kzin war 2367-2433.
- The Sol Belt possesses an abundance of valuable ores, which are easily accessible due to the low to negligible gravity of the rocks containing them. Originally a harsh frontier under U.N. control, the Belt declared independence after creating Confinement Asteroid, a habitat with spin gravity that permitted safe gestation of children, and Farmer's Asteroid, the Belt's primary food source. Almost immediately a lively competition began between the fiercely independent "Belters" and the technology police of the U.N. Several years of tension and economic conflicts followed, but soon settled into a relatively peaceful trade relationship as the Belt has so many resources that the UN and the Earth need.
- Mercury is also a colony world with a small number of inhabitants, used mainly for mining and as a gravitational anchor for orbiting solar power stations which beam power to the more remote colonies using gigantic lasers. At the time of the First Man-Kzin War, human society is so pacifistic that no weapons exist; those who are able to even contemplate killing another sentient being or constructing a weapon for that purpose are regarded as mental aberrations and must take drugs to control their thoughts. However, an enormous laser, whether constructed as a weapon or not, makes a highly effective one, and it's strongly implied that the existence of the Mercury power satellites is a large part of what enabled Sol System to hold off the Kzinti in the early part of the war.
- Down is the home world of the Grogs and a former Kzinti colony. It orbits "L5-1668", a faint, cool M-type star, significantly redder and cooler than Sol and 12.3 light-years from it. Down is made habitable in part because of its large moon, Sheila. Grogs, though friendly, are feared by humanity, due to their telepathic ability to control the minds of animals (and possibly sentient species as well). Because of this fear, humans have placed a Bussard ramjet field generator in close orbit around Down's sun, thus enabling them to destroy the Grog population should they ever take hostile action against any sentient species.
- Jinx, orbiting Sirius A, is a massive moon of a gas giant (simply called Primary), stretched by tidal forces into an egg shape, with surface gravity at the habitable areas near the limits of human extended tolerance. The poles lie in vacuum, the equatorial regions are Venus-like (and inhabited only by the Bandersnatchi); the zones between have atmosphere breathable by humans. Jinx's poles become a major in vacuo manufacturing area. Jinxian humans are short and squat, the strongest bipeds in Known Space. But they tend to die early, from heart and circulatory problems. There is a tourist industry which provides substantial useful interplanetary trade credits for the Bandersnatchi, who allow themselves to be hunted by humans under strict protocols.
- Wunderland is a planet circling Alpha Centauri, and was the earliest extra-solar colony in Known Space's human history. It has a surface gravity of 60% that of Earth's and is hospitable to human life. Wunderland was invaded and its population enslaved by the Kzinti during the first Man-Kzin War. It was freed near the end of the First War by the human Hyperdrive Armada from We Made It. The system has an asteroid belt in the shape of a crescent, which gives it its name—the Serpent Swarm. The capital asteroid, Tiamat, houses one of the largest Kzin populations in Known Space.
- We Made It, orbiting Procyon A, got its name because the first colony ship crash-landed. Gravity is about three-fifths Earth's. The planet's axis is pointed along the plane of its ecliptic (like Uranus), creating ferocious winds on the order of 500 mph (800 km/h) during half of the planet's year, forcing the people to live underground. Natives are known as "Crashlanders", tend to be very tall, and many are albinos. Their capital, which was the site of their colony ship's landing, is called Crashlanding City. We Made It also has viscous, algae-choked "oceans" and a big icy moon, ironically named Desert Isle.
- Plateau in the Tau Ceti system is Venus-like, with a plateau (called Mount Lookatthat), half the size of California, rising high enough out of the dense atmosphere to be habitable. Inhabitants ("Mountaineers") are divided into two rigid hereditary castes, the "crew" and the "colonists", depending on whether their ancestors piloted the colonizing vessel. The crew are the upper caste, and hold power through their monopoly on organ transplantation and control of the police. The original colonists signed the "Covenant of Planetfall", agreeing that this outcome was just recompense for the labors of the crew during the voyage; that they signed at gunpoint as they were awakened from hibernation is kept secret from later generations, and also that those who refused, died. This repressive system is overthrown in A Gift From Earth, and the former inequality and caste system appears to have disappeared by the time The Ethics of Madness takes place.
- Home orbits the star Epsilon Indi, about 12 light years from Earth. The planet received its name because of its remarkable similarity to Earth; its day is nearly 24 hours long and its surface gravity is a comfortable 1.08 g. Oceans, mean global temperature, seasons, and moon (Home's moon is called Metaluna, but is often referred to as "the Moon" by Homers) are also similar. According to Protector, the original colonists had planned to call their world "Flatland" as a sort of joke, but once settled on Home they had changed their minds — "a belated attack of patriotism", Elroy Truesdale of Protector muses. The entire population of Home is secretly destroyed as a consequence of Brennan's and Truesdale's war with the Pak — Brennan turns the entire population into human Protectors to create an army to fight the Pak invaders. Home is resettled quickly though, since another ramjet with colonists is already on its way when the colony "fails". In Procrustes and other later stories, Home is once again presented as a vibrant colony.
- Canyon was once an uninhabitable Mars-like world known as Warhead. It is the second of seven planets around p Eridani A, 22 light-years from Earth. It was used as a military outpost by the Kzinti, until the planet was hit by a weapon called the "Wunderland Treatymaker" during the Third War. The attack tore a long, narrow, kilometers-deep crater into the crust approximately the size of the Baja Peninsula. The air and moisture in the thin atmosphere gathered at the bottom of this artificial canyon, creating a breathable environment, complete with a sea at the bottom. The planet was then renamed for the crater, and settled by humans in a huge city running up the crater wall. Archaic (hyper-aggressive and intractable) Kzinti were entombed in stasis field shells during the attack and are still beneath the lava, and someday, somebody will have to deal with them. The attack by the Wunderland Treatymaker is detailed as a part of Destiny's Forge by Paul Chafe, a part of the Man-Kzin Wars shared universe.
- Gummidgy is a jungle world popular with hunters. It is home to the Gummidgy Orchid-Thing, a sessile carnivore which hangs from trees and is a popular trophy for the wealthy. It orbits CY Aquarii, a blue giant SX Phoenicis variable star; due to the resulting high levels of ultraviolet light, most humans (except Jinxians) require melanin-boosting medication to venture outdoors.
- Fafnir is a former Kzin colony covered almost entirely in water. When under Kzinti control it was called Shasht, a Kzin word meaning "burrowing murder." It was captured by humans during the Man-Kzin Wars. Humans and Kzinti now cohabitate. The humans prefer to live on the coral islands while the Kzinti prefer the single large continent which they continue to call Shasht.
- Margrave is a late addition to the family of Human colonies. In the Ringworld era it is still a frontier world, and is home to enormous birds the inhabitants have dubbed "rocs". It orbits Lambda Serpentis (27 Serpentis), a G0 star 34.7 light-years from Earth. It is named after its discoverer, J. Margrave Julland.
- Silvereyes is, at the time of Ringworld, the furthest Human world from Earth (21.3 light-years, 60 days at Quantum-I hyperdrive speeds), orbiting Beta Hydri. In Niven's obscure story The Color of Sunfire it has entire continents covered with Slaver sunflowers (bred as defense for Thrint manors, they focus sunlight using silver leaves as parabolic reflectors), giving it an appearance from orbit of having "silver eyes". The Man-Kzin Wars books, conversely, have it entirely covered by a world ocean, with groves of sunflowers growing up from the bottom of the ocean. The Ringworld Roleplaying Game describes it as an ocean planet dotted with island shield volcanoes.
- The Fleet of Worlds is the five (at one point six, as detailed in Fleet of Worlds) planets that are home to the Puppeteers (see above), presently being moved in formation at sub-light speeds out of the galaxy to avoid destruction as the wave of radiation from an explosion of the galactic core sweeps towards the outer reaches of the galaxy. They orbit about each other in a Klemperer rosette.
- Hearth is the homeworld of the Pierson's Puppeteers with a population of around one trillion and is covered by arcologies, most over one mile tall. Its industries and population generate so much waste heat it no longer requires a star for warmth (the four other "farmworlds" use artificial orbital lights to grow food).
- Kobold was a tiny artificial world created in the outer Sol System by Jack Brennan, a human Protector, composed of a small sphere of neutronium in the center ringed by a larger torus. Gravity generators facilitated movement between the two sections and were used in games and art. Brennan destroyed Kobold just prior to leaving for his war with the Pak Protectors.
- The Ringworld is an artificial world structure with three million times the surface area of Earth, built in the shape of a giant ring orbiting its sun, a million miles wide and with a diameter of 186 million miles. It was built by the Pak, who either abandoned it, or more likely died out much as the Earth Pak did, due to a lack of a key yamlike root which produces the conversion to Protector-stage Pak (which required a very specifically targeted soil chemistry to grow). It is inhabited by a number of different evolved hominid species, and includes representative samples of Bandersnatchi, Martians and Kzinti, and possibly other alien races that existed at the time of its construction.
- Sheathclaws is a planet colonized by humans aboard Angel's Pencil and descendants of a rogue Kzin telepath. It orbits an as-yet-unspecified star 98 light-years from Earth, and kept its existence secret for several centuries. The Patriarchy would dearly love to capture the entire population of potential Telepaths and press them into service.
- "Kzin" translates as "Home-of-the-Kzinti" or "Kzinhome" in the Hero's Tongue. It orbits 61 Ursae Majoris and has higher gravity than Earth and more oxygen in the atmosphere. It has two moons, known as the Hunter's Moon and the Traveler's Moon.
- Cue Ball is an uninhabitable ice world orbiting Beta Lyrae.
The series features a number of "superscience" inventions which figure as plot devices. Stories earlier in the timeline feature technology such as Bussard ramjets, Drouds (wires capable of directly stimulating the pleasure centers of the brain) and explore how organ transplantation technology enables the new crime of organlegging (as well as the general sociological effects of widespread transplant technology), while later stories feature hyperdrive, invulnerable starship hulls, stasis fields, molecular monofilaments, transfer booths (teleporters used only on planetary surfaces), the lifespan-extending drug boosterspice, and the tasp which is an extension of the wirehead development which works without direct contact.
The impact of inventions and technology on society is a recurring, if not central theme in Niven's work: for example, addiction to electric brain stimulation resulting in "wireheads", or the secondary and tertiary effects of an invention such as teleportation on social behavior, problems, and mores.
The milieu can be viewed as representing the last gasp of Campbell-era science fiction, as the iconoclastic, counterculture influences of "new wave" science fiction of the sixties play no part in most of the stories. However, there are notable exceptions in the Gil the ARM stories; and Jigsaw Man first appeared in Harlan Ellison's landmark "new wave" anthology, Dangerous Visions.
Organ Transplantation 
On Earth in the mid 21st century it became possible to transplant any organ from any person to another, with the exception of brain and central nervous system tissue. Individuals were categorized according to their so-called "rejection spectrum" which allowed doctors to counter any immune system responses to the new organs, allowing transplants to "take" for life. It also enabled the crime of "organlegging" which lasted well into the 24th century.
Faster Than Light (FTL) propulsion, or hyperdrive, was obtained from the Outsiders at the end of the First Man-Kzin War. In addition to winning the war for humanity, it allowed the re-integration of all the human colonies, which were previously separated by distance. Standard hyperdrive covers a distance of one light-year every three days (121.75 x c). A more advanced Quantum II Hyperdrive introduced later is able to cover the same distance in one and a quarter minutes (420,768 x c).
In Niven's first novel, World of Ptavvs, the hyperdrive used by the Thrintun required a ship to be going faster than 93% of the speed of light. However, this is the only time that Hyperdrive is described this way.
In the vast majority of Known Space material, hyperdrive requires that a ship be outside a star's gravity well to use. Ships which activate hyperdrive close to a star are likely to disappear without a trace. This effect is regarded as a limitation based on the laws of physics. In Niven's novel Ringworld's Children the Ringworld itself is converted into a gigantic Quantum II hyperdrive and launched into hyperspace while within its star's gravity well. Ringworld's Children reveals that there is life in hyperspace around gravity wells and that hyperspace predators eat spaceships which appear in hyperspace close to large masses, thus explaining why a structure as large as the Ringworld can safely engage the hyperdrive in a star's gravity well.
Stasis Fields 
A Slaver stasis field creates a bubble of space/time disconnected from the entropy gradient of the rest of the universe. Time slows effectively to a stop for an object in stasis, at a ratio of some billions of years outside to a second inside. An object in stasis is invulnerable to anything occurring outside the field, as well as being preserved indefinitely. A stasis field may be recognized by its perfectly reflecting surface, so perfect in fact that it reflects 100% of all radiation and particles, including neutrinos.
Invulnerable Hulls 
The Puppeteer firm, General Products, produces an invulnerable starship hull, known simply as a General Products Hull. The hulls are impervious to any type of matter or energy, with the exception of antimatter (which destroys the hull), gravitation, and visible light (which pass through the hull). While invulnerable themselves, this is no guarantee that the contents are likewise protected. For example, though a high speed impact with the surface of a planet or star may cause no harm to the hull, the occupants will be crushed if they are not protected by additional measures such as a stasis field or a gravity compensating field.
In Fleet of Worlds, the characters tour a General Products factory and receive clues that allow them to destroy a General Products hull from the inside using only a high-powered interstellar communications laser. In Juggler of Worlds, the Puppeteers, attempting to surmise how this was done without antimatter, identify another technique which can be used to destroy the otherwise invulnerable hulls, one which does suggest some potential defense options.
Boosterspice is a compound that increases the longevity and reverses aging of human beings. With the use of boosterspice, humans can easily live hundreds of years and, theoretically, indefinitely.
Developed by the Institute of Knowledge on Jinx, it is said to be made from genetically engineered ragweed (although early stories have it ingested in the form of edible seeds). In Ringworld's Children, it is suggested boosterspice may actually be adapted from Tree-of-Life, without the symbiotic virus that enabled hominids to metamorphose from Pak Breeder stage to Pak Protector stage (mutated Pak breeders were the ancestors of both Homo sapiens and the hominids of the Ringworld).
On the Ringworld, there is an analogous (and apparently more potent) compound developed from Tree-of-Life, but they are mutually incompatible; in The Ringworld Engineers, Louis Wu learns that the character Halrloprillalar died when in ARM custody after leaving the Ringworld, as a result of having taken boosterspice after having used the Ringworld equivalent. Boosterspice only works on Homo sapiens, whereas the Tree-of-Life compound will work on any hominid descended from the Pak.
Stepping Disks 
Stepping Disks are a fictional teleportation technology. They were invented by the Pierson's Puppeteers, and their existence is not generally known to other races until the events of The Ringworld Engineers.
The stepping disks are an outgrowth and improvement of the transfer booth technology used by humans and other Known Space races. Unlike the booths, the disks do not require an enclosed chamber, and somehow can differentiate between solid masses and air, for example. They also have a far greater range than transfer booths, extending several Astronomical Units.
Several limitations to stepping disks are mentioned in the Ringworld novels. If there is a difference in velocity between two disks, any matter transferred between them must be accelerated by the disk accordingly. If there is not enough energy to do so, the transfer cannot take place. This becomes a problem with disks that are a significant distance apart on the Ringworld surface, as they will have different velocities: same speed, different direction.
Transfer Booths 
Transfer Booths are an inexpensive form of teleportation. They are similar in appearance to an old style telephone booth: one enters, "dials" one's desired destination, and is immediately deposited in a corresponding booth at the destination. They are inexpensive: a trip anywhere on Earth costs only a "tenth-star" (presumably equivalent to a dime). Introduced by one of Gregory Pelton's ancestors, apparently bought from and based on Puppeteer technology.
The ARM is the police force of the United Nations. ARM originated as an acronym for "Amalgamation of Regional Militia", though this is not a term in current usage by the time of the Known Space novels. An agent of the ARM, Gil Hamilton, is the protagonist of Niven's sci-fi detective stories, a series-within-a-series gathered in the collection Flatlander (Confusingly, "Flatlander" is also the name of an unrelated Known Space story.)
Their basic function is to enforce mandatory birth control on overcrowded Earth, and restrict research which might lead to dangerous weapons. In short, the ARM hunts down women who have illegal pregnancies and suppresses all new technologies. They also hunt organleggers, especially in the era of the "organ bank problem". Among the many technologies they control and outlaw are all trained forms of armed and unarmed combat. By the 25th century, ARM agents were kept in an artificially induced state of paranoid schizophrenia to enhance their usefulness as law enforcement officials, which led to them sometimes being referred to as "Schizes". Agents with natural tendencies toward paranoia were medicated into docility during their off duty hours, through the aforementioned science of psychistry (see Madness Has Its Place and Juggler of Worlds).
Their jurisdiction is limited to the Earth-Moon system; other human colonies have their own militia. Nevertheless, in many Known Space stories, ARM agents operate or exert influence in other human star systems through the "Bureau of Alien Affairs" (see In the Hall of the Mountain King, Procrustes, The Borderland of Sol, and "Neutron Star"). These interventions begin following the Man-Kzin Wars and the introduction of hyperdrive, presumably as part of a general re-integration of human societies.
Stories in Known Space 
Unlike many fictional universes, the component tales of Known Space were largely released as short stories or serials in various science fiction anthology magazines. These stories were generally subsequently released in one or more collection volumes. To add some further confusion, some of the shorter novels published in magazines were later expanded to, or incorporated in, book-length novels. Due to the large number of stories, it is particularly difficult for a completionist fan to read every story in the series. There are also two or three short stories which share common themes and some background elements with Known Space stories, but which are not considered a part of the Known Space universe: Bordered in Black and One Face (see the collection Convergent Series), and possibly The Color of Sunfire.
In the Known Space stories, Niven had created a number of technological devices (GP hull, stasis field, Ringworld material) which, combined with the "Teela Brown gene", made it very difficult to construct engaging stories beyond a certain date — the combination of factors made it tricky to produce any kind of creditable threat/problem without complex contrivances. Niven demonstrated this, to his own satisfaction, with Safe at Any Speed. After 1975, he began to write significantly fewer Known Space stories. However, Niven later invited other authors to participate in a series of shared-universe novels, with the Man-Kzin Wars as their setting.
Stories by Niven 
|"The Coldest Place"||1964||Worlds of If||Tales of Known Space|
|"World of Ptavvs"||1965||Worlds of Tomorrow||—|
|"Becalmed in Hell"||1965||The Magazine of Fantasy and Science Fiction||Tales of Known Space, All the Myriad Ways, Playgrounds of the Mind|
|"Eye of an Octopus"||1966||Galaxy Magazine||Tales of Known Space|
|"The Warriors"||1966||Worlds of If||Tales of Known Space, Man-Kzin Wars I|
|"Neutron Star"||1966||Worlds of If||Neutron Star, Crashlander|
|"How the Heroes Die"||1966||Galaxy Magazine||Tales of Known Space|
|"At the Core"||1966||Worlds of If||Neutron Star, Crashlander|
|"A Relic of the Empire"||1966||Worlds of If||Neutron Star, Playgrounds of the Mind|
|"At the Bottom of a Hole"||1966||Galaxy Magazine||Tales of Known Space|
|"The Soft Weapon"||1967||Worlds of If||Neutron Star, Playgrounds of the Mind|
|"Flatlander"||1967||Worlds of If||Neutron Star, Crashlander|
|"The Ethics of Madness"||1967||Worlds of If||Neutron Star|
|"Safe at any Speed"||1967||The Magazine of Fantasy and Science Fiction||Tales of Known Space|
|"The Adults"||1967||Galaxy Magazine||—|
|"The Handicapped"||1967||Galaxy Magazine||Neutron Star|
|"The Jigsaw Man"||1967||Dangerous Visions||Tales of Known Space|
|"Slowboat Cargo"||1968||Worlds of If||—|
|"The Deceivers"||1968||Galaxy Magazine||Tales of Known Space|
|"Grendel"||1968||(collection only)||Neutron Star, Crashlander|
|"There is a Tide"||1968||Galaxy Magazine||Tales of Known Space, A Hole in Space|
|World of Ptavvs||1968||(novel)||—|
|A Gift From Earth||1968||(novel)||—|
|"Wait It Out"||1968||Futures Unbounded||Tales of Known Space|
|"The Organleggers"||1968||Galaxy Magazine||The Shape of Space, The Long ARM of Gil Hamilton, Flatlander|
|Ringworld||1970||(novel)||Nebula Award winner, 1970;
Hugo Award winner, 1971;
Locus Award winner, 1971
|"Cloak of Anarchy"||1972||Analog Science Fiction||Tales of Known Space, N-Space|
|Protector||1973||(novel)||Hugo Award nominee, 1974;
Locus Award nominee, 1974
|"The Defenseless Dead"||1973||(collection only)||The Long ARM of Gil Hamilton, Playgrounds of the Mind|
|"The Borderland of Sol"||1975||Analog Science Fiction||Tales of Known Space, Crashlander, Playgrounds of the Mind|
|"ARM"||1975||Epic||The Long ARM of Gil Hamilton|
|The Ringworld Engineers||1980||(novel)||Hugo Award nominee, 1981;
Locus Award nominee, 1981
|The Patchwork Girl||1980||(novel)||also Flatlander|
|"Madness Has Its Place"||1990||(collection only)||Man-Kzin Wars III, Three Books of Known Space|
|"Ghost"||1994||(framing story, collection only)||Crashlander|
|"The Woman in Del Rey Crater"||1995||(collection only)||Flatlander|
|The Ringworld Throne||1996||(novel)||—|
|"Choosing Names"||1998||(collection only)||Man-Kzin Wars VIII|
|"Fly-By-Night"||2002||(collection only)||Man-Kzin Wars IX|
|"The Hunting Park"||2005||(collection only)||Man-Kzin Wars XI|
|Fleet of Worlds
(co-authored with Edward M. Lerner)
|Juggler of Worlds
(co-authored with Edward M. Lerner)
|Destroyer of Worlds
(co-authored with Edward M. Lerner)
|Betrayer of Worlds
(co-authored with Edward M. Lerner)
|Fate of Worlds
(co-authored with Edward M. Lerner)
(Note that most stories appeared in more than one collection; they may not all be listed here.)
Man-Kzin Wars 
Niven has described his fiction as "playground equipment", encouraging fans to speculate and extrapolate on the events described. Debates have been made, for example, on who built the Ringworld (Pak Protectors and the Outsiders being the traditional favorites, but see Ringworld's Children for a possibly definitive answer), and what happened to the Tnuctipun. However, Niven also states that this is not an invitation to violate his copyrights, so fans should try to avoid publishing works that are too obviously based in the Known Space universe without Niven's given permission.
Niven was also reported to have said that "Known Space should be seen as a possible future history told by people that may or may not have all their facts right."
The author also published an "outline" for a story which would "destroy" the Known Space Series (or more precisely, reveal much of the Known Space background to be an in-universe hoax), in an article entitled "Down in Flames". Although the article is written as though Niven intended to write the story, he later wrote that the article was only an elaborate joke, and he never intended to write such a novel. The article itself notes that the outline was made obsolete by the publication of Ringworld. "Down in Flames" was a result of a conversation between Norman Spinrad and Niven in 1968, but at the time of its first publication in 1977 some of the concepts were invalidated by Niven's writings between '68 and '77. (A further edited version of the outline was published in N-Space in 1990.)
- Larry Niven, "The Warriors," Tales of Known Space (Del Rey, 1985), 261
- Hal Colebatch "Catspaws", in Man-Kzin Wars XI
- p.76, Wayne Douglas Barlowe, Barlowe's Guide to Extraterrestrials: Great Aliens from Science Fiction Literature, Workman Pub Co, 1979
- p.100, Wayne Douglas Barlowe, Barlowe's Guide to Extraterrestrials: Great Aliens from Science Fiction Literature, Workman Pub Co, 1979
- Paul Chafe Destiny's Forge
- John Hewitt et al., Larry Niven's Ringworld: Roleplaying Adventure Beneath the Great Arch, Chaosium Inc., 1984.
- The cover of Tales of Known Space: The Universe of Larry Niven, Del Rey, 1975 (at least 10 printings), has this as "L5-1665"
- This is almost certainly a corruption of BD+05 1668 (a.k.a. LHS 33), another name for Luyten's Star
- Larry Niven, Protector (Ballantine Books, 1973), 183
- Larry Niven, Edward M. Lerner, Destroyer of Worlds (Tor Books, 2009), 284
- Oddly, the Ringworld Roleplaying book places it around Fomalhaut instead, in contradiction with primary sources such as Niven's Grendel short story.
- Expanded and republished as a novel in 1968
- Expanded and republished as Protector in 1973.
- Expanded and republished as A Gift From Earth in 1968.
- Subsequently renamed "Intent to Deceive"
- Subsequently renamed "Death by Ecstasy"
- "1970 Award Winners & Nominees". Worlds Without End. Retrieved 2009-07-20.
- "1971 Award Winners & Nominees". Worlds Without End. Retrieved 2009-07-20.
- "1974 Award Winners & Nominees". Worlds Without End. Retrieved 2009-07-20.
- "1981 Award Winners & Nominees". Worlds Without End. Retrieved 2009-07-20.
- "Future Histories", The Bulletin of the Science Fiction Writers of America, Summer 1989, Vol. 23 #2, issue 104
- Larry Niven Official Site
- Encyclopedia of Known Space
- The Incompleat Known Space Concordance
- Timeline of the Known Space universe
- Marc Carlson's Timeline of the Known Space universe
- Website for the Man-Kzin Wars novel Destiny's Forge
- Homepage of MKW author Paul Chafe