Reduviidae (assassin bugs) is the second largest family of the hemipteran suborder Heteroptera (true bugs). The family contains 25 subfamilies, the largest number amongst true bugs, and 28 tribes. Most previously published keys do not include all recognized subfamilies and even complete keys lead to incorrect identification of certain taxa. We here present a comprehensive and well-illustrated identification key to subfamilies and tribes (except Emesinae) of Reduviidae. The key is complemented by taxon treatments that provide, for each subfamily, diagnostic features, notes on taxonomy and distribution, a comment on taxa occurring in Canada, natural history notes, and a short bibliography.