Ants belonging to the genus Gnamptogenys are important and diverse predators in the forests of the tropics of the Americas, Southeast Asia and Australasia. The recent rapid accumulation of these ants in collections rendered the last revision obsolete, raising the number of known species from about 80 to over a 120 species worldwide. The present study recognizes 49 Old World species, almost half of them new, distributed among 5 species groups. They are present in many entomological collections as the large size of some species and their conspicuousness has caught the attention of even general collectors. They figure increasingly in studies of diversity and ecology due to aspects of their biology such as predatory specialization or their reproduction which includes proper queens in some species and worker reproduction in other species. While most species are ground nesters in forests, some are arboreal and others are subterranean. This revision covers all the Old World species and proposes phylogenetic relations among the different species groups. The identification of the species is possible with aid of well-illustrated keys for workers and queens. The results of working with the keys can be rapidly confirmed by consulting the diagnosis that accompanies each species account, or the full description if need be. The phylogenetic analysis uses a valuable series of internal morphological characters previously unconsidered in ant systematics. Detailed distribution data is also included for each species. This work will be valuable for those studying insect diversity and ecology of forests in Southeast Asia and Australasia. Their diverse biology and relative large size of many species make these ants attractive subjects for comparative studies and this reference should open the door for further studies.