A summary classification of 175 modern species and 30 well-represented fossil forms of waterfowl (Aves: Anseriformes) is presented, based on a series of phylogenetic (cladistic) analyses of the group using morphological characters (Livezey, 1986a, 1986b, 1986c, 1989a, 1989b, 1990, 1991, 1993a, 1993b, 1995a, 1995b, 1995c, 1996a, 1996b, 1996c, 1997a, 1997b). The proposed classification includes a superordinal grouping with the Order Galliformes, and subdivides the Anseriformes into two suborders (Anhimae and Anseres), two superfamilies (Anseranatoidea and Anatoidea), and five families (Anhimidae, Anseranatidae, †Presbyornithidae, †,Cnemiornithidae, and Anatidae). Among the latter, the Anatidae is the largest and comprises six subfamilies: Dendrocygninae (comprising two tribes and two genera), Dendrocheninae (two genera), Anserinae (four tribes, nine genera), Stictonettinae (one genus), Tadorninae (four tribes, 15 genera), and Anatinae (five tribes, 31 genera). The classification also incorporates: phylogenetic inferences and associated taxonomic decisions subsequent to the preliminary work by Livezey (1986a); corrections of classifications included with the earlier analyses; recognition of two species of comb-duck (Sarkdiornis); and provisional partitions of several problematic species groups (Branta canadensis, Merganetta armata, and Somateria mollissima). Also included are a concise historical review of the classification of the order, an assessment of the relative support documented for the taxonomic groups defined within the classification, and suggestions for future investigations.