A taxonomic revision of the genus Gnamptogenys Roger in Southeast Asia and Australasia, based on the workers, recognizes forty nine species, twenty five of which are new, as follows: G. albiclava (Mann), G. aterrima (Mann), G. atrata sp. n., G. bicolor (Emery), G. biloba sp. n., G. binghamii (Forel), G. biroi (Emery), G. bulbopila sp. n., G. chapmani Brown, G. costata (Emery), G. coxalis (Roger), G. crassicornis (Forel), G. crenaticeps (Mann), G. cribrata (Emery), G. delta sp. n., G. epinotalis (Emery), G. fistulosa sp. n., G. gabata sp. n., G. gastrodeia sp. n., G. grammodes Brown, G. helisa sp. n., G. hyalina sp. n., G. lacunosa sp. n., G. laevior (Forel), G. leiolabia sp. n., G. lucida (Mann), G. luzonensis (Wheeler), G. macretes Brown, G. major (Emery), G. malaensis (Mann), G. meghalaya sp. n., G. menadensis (Mayr), G. niuguinense sp. n., G. ortostoma sp. n.,G. palamala sp. n.,G. panda (Brown), G. paso sp. n., G. pertusa sp. n., G. polytreta sp. n., G. posteropsis (Gregg), G. preciosa sp. n., G. rugodens sp. n., G. scalpta sp. n., G. sichuanensis sp. n., G. sila sp. n., G. sinensis Wu and Xiao, G. solomonensis sp. n., G. taivanensis (Wheeler), and G. treta sp. n. Five new synonymies are proposed: G. bicolor = G. bannana Xu and Zhang; G. crassicornis = G. spiralis (Karavaiev); G. cribrata = G. diehlii (Forel) = G. dammermani (Wheeler); G. laevior = G. kalabit Brown. Keys, illustrations, and species accounts are provided. Five species groups are recognized. A phylogenetic analysis for nineteen terminal taxa and sixty morphological characters using parsimony was carried out with PAUP, using the following taxa as outgroups: Heteroponera Mayr, Platythyrea Roger, and Myrmica incompleta Provancher. Four Old World Gnamptogenys species groups, as well as five individual species of a weakly supported clade were part of the ingroup. Additional ingroup taxa included five New World species of Gnamptogenys, Ectatomma F. Smith, and the hytidoponera impressa group. Monophyly of a clade formed by the genera Ectatomma, Rhytidoponera Mayr, and Gnamptogenys Roger is strongly supported. Monophyly of Gnamptogenys is supported by loss of a fore tibial seta. Neotropical taxa form sister relationships with Old World lineages at several points in the tree.