Children and adolescents who are growing up gay, lesbian, bisexual, gender nonconforming, or gender discordant experience unique developmental challenges. They are at risk for certain mental health problems, many of which are significantly correlated with stigma and prejudice. Mental health professionals have an important role to play in fostering healthy development in this population. Influences on sexual orientation, gender nonconformity, and gender discordance, and their developmental relationships to each other, are reviewed. Practice principles and related issues of cultural competence, research needs, and ethics are discussed.