A total of 44 species are placed in the genus Dacus in South-east Asia and divided amongst four subgenera, viz. Callantra Walker, Dacus Fabricius, Didacus Collart and Leptoxyda Macquart. In all, 27 species are revised and the following 17 new species described: Dacus (Callantra) ambonensis, D. (C.) atrimarginatus, D. (C.) calirayae, D. (C.)feijeni, D. (C.) insulosus, D. (C.) lagunae, D. (C.) leongi, D. (C.) maculipterus, D. (C.) murphyi, D. (C.) nanggalae, D. (C.) ooii, D. (C.) ramanii, D. (C.) siamensis, D. (C.) tenebrosus, D. (C.) vijaysegarani, D. (C.) wallacei, Dacus (Dacus) santongae. A key to species within the genus Dacus is presented based on characters that bypass subgeneric groupings, because of the present uncertainty of subgeneric limits. Information is given on location of type specimens, host plants, attractant records and geographic distributions. Lectotypes are designated for D, conopsoides de Meijere, D. esakii (Shiraki), D, icariiformis Enderlein and D, persicus Hendel. Thirteen new synonymies within Dacus are established: Callantra ihai Shiraki [of Dacus esakii (Shiraki)]; Callantra smieroides Walker, Mellesis destillatoria Bezzi, Mellesis eumenoides Bezzi, Mellesis bioculata Bezzi, Callantra unifasciatus Hardy, Callantra variegata Wang (all of Dacus longicornis Wiedemann); Mellesis apicalis Shiraki [of Dacus nummularius (Bezzi)]; Callantra munroi Zaka-ur-Rab, Callantra nepalensis Hardy, Callantra quadristriata Munro [all of Dacus polistiformis (Senior-White)]; Callantra ziae Wang [of Dacus satanas (Hering)]; Dacus cocciniae Premlata & Awtar Singh (of Dacus ciliatus Loew). Dacus persicus Hendel is removed from synonymy with D. longistylus Wiedemann. Sinodacus fuscans Wang is placed as a new synonym of Bactrocera brachycera (Bezzi).