Inisheer (Irish: Inis Oírr, the island's official name, Inis Oirthir, meaning "east island", and traditionally Inis Thiar, meaning "rear island") is the smallest and most eastern of the three Aran Islands in Galway Bay, Ireland. Inisheer has a population of about 297, making it the second smallest of the Aran Islands in terms of population.
The official name, Inis Oírr, was brought into usage by the Ordnance Survey Ireland. It may be a compromise between the traditional local name Inis Thiar and the previous official name Inis Oirthir. There is no Irish word corresponding to the second element in the official name. It seems from the annals that the island's name always contained the element iarthar or thiar in the sense of "rear or back island" and not "west" as is the usual sense of this word. The form Inis Oirthir, used by the 17th century scholar Ruaidhrí Ó Flaithbheartaigh, seems to have arisen out of his own misreading of the annals.
Geology and geography 
The limestones date from the Visean period (Lower Carboniferous), formed as sediments in a tropical sea approximately 350 million years ago, and compressed into horizontal strata with fossil corals, crinoids, sea urchins and ammonites.
Glaciation following the Namurian phase facilitated greater denudation. The result is that Inisheer is one of the finest examples of a Glacio-Karst landscape in the world. The effects of the last glacial period (the Midlandian) are most in evidence, with the island overrun by ice during this glaciation. The impact of earlier Karstification (solutional erosion) has been eliminated by the last glacial period, so any Karstification now seen dates from approximately 10,000 years ago and the island Karst is thus recent.
Solutional processes have widened and deepened the grykes of the limestone pavement. Pre-existing lines of weakness in the rock (vertical joints) contribute to the formation of extensive fissures separated by clints (flat pavement like slabs). The rock karstification facilitates the formation of sub-terrainean drainage.
Climate and agriculture 
The island has an unusually temperate climate. Average air temperatures range from 15°C in July to 6°C in January. The soil temperature does not usually drop below 6°C (end 2010 recorded a prolonged period of snow, the first in living memory). Since grass will grow once the temperature rises above 6°C, this means that the island (like the neighbouring Burren) has one of the longest growing seasons in Ireland or Britain, and supports diverse and rich plant growth. Late May is the sunniest time, and also likely the best time to view flowers, with the gentians and avens peaking (but orchid species blooming later).
Flora and fauna 
The island supports arctic, Mediterranean and alpine plants side-by-side, due to the unusual environment. Like the Burren, the Aran islands are renowned for their remarkable assemblage of plants and animals. The grikes (crevices) provide moist shelter, thus supporting a wide range of plants including dwarf shrubs. Where the surface of the pavement is shattered into gravel, many of the hardier Arctic or Alpine plants can be found. But when the limestone pavement is covered by a thin layer of soil, patches of grass are seen, interspersed with plants like the gentian and orchids. Notable insects present include the butterfly the Pearl-bordered Fritillary Boloria euphrosyne, Brown Hairstreak Thecla betulae, Marsh Fritillary Euphydryas aurinia and Wood White Leptidea sinapis; the moths, the Burren Green Calamia tridens, Irish Annulet Odontognophos dumetata and Transparent Burnet Zygaena purpuralis; and the hoverfly Doros profuges.
The island has a medieval O'Brien castle built in an ancient stone fort on top of the hill, and various church ruins including a church named Teampall Chaomháin, which has to be uncovered annually as the floor of it is well below the level of the sand.
The cargo vessel Plassey was shipwrecked off Inis Oírr in the 1960s, and has since been thrown above high tide mark at Carraig na Finise on the island by strong Atlantic waves. The islanders rescued the entire crew from the stricken vessel using a breeches buoy- an event captured in a pictorial display at the National Maritime Museum in Dún Laoghaire, County Dublin.
Irish is still today the daily language of the 300 residents. In addition, many school pupils come to the island to learn Irish in an environment where it is a living language.
In the media 
- Ó Murchú (Séamas): An tainm áite Inis Oírr in Éigse 26 (1992), pp. 119–123.
- D.A. Webb, 'Noteworthy Plants of the Burren', 1961, Proceedings of the Royal Irish Academy. Section B: Biological, Geological, and Chemical Science