The progression from adolescence to adulthood is a time of tremendous change, characterized by issues of identity formation, autonomy, and shifting relationship dynamics. The family is embedded in all aspects of this transition and serves as both a protective support and a limiting factor, a complicated duality that raises psychological, ethical, and legal issues. This article discusses the influence of familial factors and provides assessment strategies for evaluating the family in relation to treatment of transitional age youth. It is increasingly evident that family engagement is a significant contributor to outcomes for transitional age youth seeking mental health treatment.