A phylogeny of blue butterflies of the genus Maculinea and related genera (Lycaenidae) is proposed, based on 91 morphological and ecological characters. The resulting tree shows that: (1) Phengaris is a derived group nested within Maculinea; (2) the Maculinea-Phengaris clade is probably nested within Glaucopsyche; (3) there are three well supported groups within the Maculinea-Phengaris clade: (alcon group ((teleius group) (arion-Phengaris group))). Some species (M. alcon, M. arionides) appear to be non-monophyletic and require reclassification. The two alternative strategies of parasitic myrmecophily in the Maculinea-Phengaris clade, viz., "predatory" and "cuckoo", seem to be derived characters of the alcon group, and of the teleius and arion-Phengaris groups, respectively. The common ancestor of Maculinea used dorsal nectary organ secretions for ant attraction, while this trait was reduced in the ancestor of the alcon group and in M. nausithous (of the teleius group). The three recent Maculinea lineages utilize taxonomically diverse host plants, the asterid families Gentianaceae (alcon and arion-Phengaris groups), Lamiaceae (arion-Phengaris group), Campanulaceae (arion-Phengaris group), and the rosid family Rosaceae (teleius group).