Cass's Homosexual Identity Formation Model (1979) is one of the most well-known and well-referenced models of identity development for gay males and lesbians. This article provides a review of Cass's six steps of the model, as well as research support for and critiques of the model. As the model was developed more than 30 years ago, the applicability of the model for today's youth is explored and implications for practitioners are discussed.