Nelson (1994) recognised six families, but subsequently (2006) included four families in Osteoglossiformes. Species are found in tropical fresh waters from South East Asia to Australia, and Africa and South America (Nelson 2006). Members from one family are found in Australia. Relationships are discussed in Lauder & Liem (1983) and Li & Wilson (1996). Several fossil groups are known.
Lauder, G.V. & Liem, K.F. 1983. The evolution and interrelationships of the actinopterygian fishes. Bulletin of the Museum of Comparative Zoology, Harvard 150: 95–197
Li, G.-Q. & Wilson, M.V.H. 1996. Phylogeny of Osteoglossomorpha. pp. 163-174 in Stiassny, M.L.J., Parenti, L.R. & Johnson, G.D. (eds). Interrelationships of Fishes. San Diego : Academic Press 496 pp.
Nelson, J.S. 1994. Fishes of the World. New York : John Wiley & Sons 600 pp.
Nelson, J.S. 2006. Fishes of the World. Hoboken, New Jersey : John Wiley & Sons, Inc. 601 pp.