The 101 Mecyclothorax carabid beetle species of Tahiti, French Polynesia comprise a very diverse adaptive radiation. Given Tahiti?s surface area of only 1,045 km2, the island?s Mecyclothorax fauna represents the densest, most diverse radiation of species on Earth. Speciation of Tahitian Mecyclothorax has also occurred very rapidly, with closely-related species allopatrically distributed across geographic ranges defined by Tahiti?s incredibly complex geological topography. Such high levels of endemism are useful for conservation management, as continuing presence of these beetles in small areas of Tahitian forest can signify good health of the native biota in those areas. This taxonomic revision includes dichotomous keys and diagnostic photographs supporting identification of all 101 species, over one-quarter newly described in this publication. Each species treatment includes ecological and geographical information. This monograph illuminates an important component of Tahitian biodiversity in support of ongoing efforts to conserve Tahiti?s biological resources.