In male crustaceans—unlike vertebrates—the endocrine and gametogenic functions are clearly separated into distinct organs, the androgenic gland and the testis, respectively. The androgenic gland is thought to be the exclusive source of hormone responsible for sex-differentiation and sexual characteristics in crustaceans. Information on this unique crustacean organ is revised with respect to its structure, secretion and role in the regulation of the expression of sexual characteristics, and intersexuality. Several decapod models are presented for research on sexual differentation in higher crustaceans.