Characiformes form part of a series called Otophysi within the superorder Ostariophysi. Otophysi contains four other orders, Cypriniformes,Siluriformes, and Gymnotiformes. Characiformes forms a group known as Characaphysi with Siluriformes and Gymnotiformes. Characiformes is the sister group to the orders Siluriformes and Gymnotiformes, though this has been debated in light of recent molecular evidence.
Originally the characins were all grouped within a single family, the Characidae. Since then 18 different families have been separated out. However, classification varies somewhat, and the most recent (2011) study confirms the circumscribed Characidae as monophyletic