The family Syrphidae (Diptera) has around 6000 species worldwide, including many species commonly seen hovering over flowers where they feed and seek possible mates. Many of the genera mimic bees or wasps, thus sharing a similar habitus, and their identification can prove difficult without a proper identification key. To aid in the identification of Syrphidae, the first chapter of the thesis presents an online interactive photographic key to the nearctic genera of Syrphidae, richly illustrated with field and laboratory images. One of the most speciose genera of the family is Ocyptamus Macquart, 1834, with around 300 species described. Recent studies suggest that Ocyptamus is paraphyletic with regards to the genera Eosalpingogaster Hull, 1949 and Toxomerus Macquart, 1855. The second chapter addresses this paraphyly through a phylogenetic analysis, based on morphological and molecular data, of 63 species currently or previously placed in the genus Ocyptamus. A monophyletic Ocyptamus was defined on the basis of cladistic principles, six new genera (Fragosa, Hypocritanus, Maiana, Nuntianus, Relictanum and Victoriana) were proposed and 10 names (Atylobaccha, Calostigma, Hermesomyia, Hybobathus, Mimocalla, Orphnabaccha, Pelecinobaccha, Pipunculosyrphus, Pseudoscaeva and Styxia) were ressurected. The third chapter considers the clade made up of Pelecinobaccha, Relictanum and Atylobaccha, revising the genera Pelecinobaccha and Relictanum, including 24 new species, 28 synonimized names, an identification key and distribution maps.