The present state of knowledge about hydrophilid genera is outlined, and comments are given on the taxonomic history of the group, generic concepts in the family, and criteria for establishing new genera. Fifteen new genera are described for 31 new and one known species: Grodum gen. n. erected for G. striatum sp. n. (type of genus) and G. endroedyi, both from South Africa; Phelea gen. n. erected for P breviceps sp. n. from Tasmania; Enigmata gen. n. erected for E. brunnea sp. n. from Madagascar; Quadriops gen. n. erected for Q. depressus sp. n. (type of genus) from Ecuador and Peru, Q. dentatus sp. n. from Venezuela, Q. politus sp. n. from Peru, Q. similaris sp. n. from Venezuela and British Guiana, and Q. reticulatus sp. n. from Costa Rica and Panama; Megagraphydrus gen. n. erected for M. politus sp. n. from Taiwan, M. jaechi sp. n. from Peninsular Malaysia, M. siamensis sp. n. (type of genus) from Thailand, M. regularis from Thailand, and M. attenuatus from Vietnam; Enochrella gen. n. erected for E. aberrans sp. n. from the Philippines; Pseudorygmodus gen. n. erected for Cylorygmus flintispangleri Moroni from Chile; Afrotormus gen. n. erected for A. metallescens sp. n. (type of genus) and A. minutus, both from South Africa; Toma gen. n. erected for T. pusilla sp. n. from West Africa to Zambia; Lulu gen. n. erected for L. sagitta sp. n. from Brazil; Platycyon gen. n. erected for P. striatus sp. n. from Papua New Guinea, P. wauensis sp. n. (type of genus) from Papua New Guinea, P. confusus from Irian Jaya, P. subopacus sp. n. from New Britain, P. superficialis sp. n. from New Britain and New Ireland, and P. reticulatus sp. n. from New Guinea; Kahanga gen. n. erected for K. inconspicua sp. n. from Peninsular Malaysia; Colerus gen. n. erected for C. fascicularis sp. n. from Madagascar; Bolbonotum gen. n. erected for B. raigrum sp. n. from Philippines, B. myophallus sp. n. (type of genus) from Malaysia (Sarawak) and Indonesia, and B. oosternoides from Thailand; Delimetrium gen. n. erected for D. sericeum sp. n. from South Africa. Six genera are placed in the subfamily Hydrophilinae: Grodum, Phelea and Enigmata in the tribe Anacaenini; Quadriops, Megagraphydrus and Enochrella in the tribe Hydrophilini (subtribe Acidocerina). The remaining genera are placed in the subfamily Sphaeridiinae: Pseudorygmodus in the tribe Rygmodini; Afrotormus in the tribe Tormissini; Toma in the tribe Coelostomatini; Lala in the tribe Omicrini; Platycyon, Kahanga, Colerus, Bolbonotum and Delimetrium in the tribe Megasternini.