Beauchêne Island is the most isolated of the Falkland Islands archipelago and until the authors' visit there in 1980 little was known or published about the island and its biota apart from its avifauna. The first collections and identifications of various plant and invertebrate groups were made and a brief account of their ecology and interrelationships is given; many of the arthropods are first records for the Falkland Islands and some are new to science. More detailed information is presented for tussock grass (or tussac), Poa flabellata, which reaches a height of 3.5 m and covers two‐thirds of the island with a unique monospecific grassland. The underlying deep peat, in places reaching 13 m depth, was investigated and radiocarbon dates obtained at various levels through the profile, indicating that the grassland has existed virtually unchanged for 12 500 years. The status of the avifauna was assessed. The black browed albatross and rockhopper penguin colonies were counted reasonably accurately and calculated to contain up to 170000 and 300000 pairs, respectively. A population of about 250 striated caracaras was counted, together with 67 nests, possibly the largest concentration of these rare raptors anywhere. The recently discovered population of fairy prions was estimated at several thousand birds. Sea lions were not abundant and fur seals, once said to occur in large numbers on the island, were absent. The biological simplicity of the exceptionally uniform tussac ecosystem offers ideal conditions for testing ecological hypotheses, especially those related to trophodynamics and predator‐prey interrelationships, and its potential for research is emphasized. The importance of applying strict conservation measures to protect this unique island is stressed in view of the possible future economic development of the Falkland Islands.