The small waterstriders of the subfamily Trepobatinae have radiated extensively on New Guinea and surrounding archipelagos. The present contribution is the first in a series of reports dealing with this endemic fauna, and presents a revised tribal level classification for the Trepobatinae, with the following new tribes proposed: Metrobatini, type genus Metrobates Uhler; Naboandelini, type genus Naboandelus Distant; Stenobatini, type genus Stenobates Esaki; Trepobatini, type genus Trepobates Uhler. A key to the tribes is provided, followed by a taxonomic treatment of the new tribe Metrobatini and its constituent genera. The following new taxa are proposed within Metrobatini: Andersenella gen. n., monobasic, type species Andersenella binotata sp. n.; Metrobatoides gen. n., monobasic, type species Metrobatoides genitalis sp. n.; Ciliometra gen. n., including type species Ciliometra kiunga sp. n., plus Ciliometra femorata sp. n. and Ciliometra sepik sp. n.; Iobates gen. n., including type species Metrobatopsis affinis Esaki (as Iobates affinis, comb. n.), plus Iobates salaw ati sp. n. and Iobates somare sp. n.; Stygiobates gen. n., including type species Stygiobates iriana sp. n., plus Stygiobates morotai sp. n.; Metrobatopsis insularis sp. n., Metrobatopsis mussau sp. n., Metrobatopsis lannae sp. n. and Metrobatopsis browni sp. n. in the previously described genus Metrobatopsis Esaki. The genus Metrobatopsis and previously included species Metrobatopsis flavonotatus Esaki and Metrobatopsis solomonensis Hungerford & Matsuda are redescribed. Habitat and distributional notes are given for all the above taxa, accompanied by figures of key characters and distribution maps.