Esperanto () is the most widely spoken constructed international auxiliary language. L. L. Zamenhof, a Polish-Jewish ophthalmologist, created Esperanto in the late 19th century and published the first book detailing it, Unua Libro, in 1887 under the pseudonym Dr. Esperanto, Esperanto translating as "one who hopes". Zamenhof's goal was to create an easy and flexible language that would serve as a universal second language to foster peace and international understanding. His original title for the language was simply the international language (lingvo internacia), but early speakers grew fond of the name Esperanto and began to use it as the name for the language in 1889; the name quickly gained prominence and has been used as an official name ever since.
In 1905, Zamenhof published Fundamento de Esperanto as a definitive guide to the language. Later that year, he organized the first World Esperanto Congress, an ongoing annual conference, in Boulogne-sur-Mer, France. The first congress ratified the Declaration of Boulogne, which established several foundational premises for the Esperanto movement. One of its pronouncements is that Fundamento de Esperanto is the only obligatory authority over the language. Another is that the Esperanto movement is exclusively a linguistic movement and that no further meaning can ever be ascribed to it. Zamenhof also proposed to the first congress that an independent body of linguistic scholars should steward the future evolution of Esperanto, foreshadowing the founding of the Akademio de Esperanto, in part modeled after the Académie française, which was established soon thereafter. Since 1905, congresses have been held in various countries every year, with the exceptions of years during the World Wars. In 1908, a group of young Esperanto speakers led by Hector Hodler established the Universal Esperanto Association, in order to provide a central organization for the global Esperanto community.
Esperanto grew throughout the 20th century, both as a language and as a linguistic community. Despite speakers facing persecution in regimes such as Nazi Germany and the Soviet Union under Stalin, Esperanto speakers continued to establish organizations and publish periodicals tailored to specific regions and interests. In 1954, the United Nations granted official support to Esperanto as an international auxiliary language in the Montevideo Resolution. Several writers have contributed to the growing body of Esperanto literature, including William Auld, who received the first nomination for the Nobel Prize in Literature for a literary work in Esperanto in 1999, followed by two more in 2004 and 2006. Esperanto-language writers are also officially represented in PEN International, the worldwide writers association, through Esperanto PEN Centro.
Esperanto has continued to develop in the 21st century. The advent of the Internet has had a significant impact on the language, as learning it has become increasingly accessible on platforms such as Duolingo and as speakers have increasingly networked on platforms such as Amikumu. With approximately two million speakers, a small portion of whom are native speakers, it is the most widely spoken constructed language in the world. Although no country has adopted Esperanto officially, Esperantujo is the collective name given to places where it is spoken, and the language is widely employed in world travel, correspondence, cultural exchange, conventions, literature, language instruction, television and radio broadcasting.
While many continue to hope for the day that Esperanto becomes officially recognized as the international auxiliary language, an increasing number have stopped focusing on this goal and instead view the Esperanto community as a "stateless diasporic linguistic minority" based on freedom of association, with a culture worthy of preservation based on its own merit. Some have also chosen to learn Esperanto due to its purported help in third language acquisition.