Sexual and Gender Expansive Youth in Foster Care: This chapter outlines the unique needs, experiences, and outcomes of sexual and gender expansive youth in the foster care system, and presents best practices for working with this vulnerable population. Definitions of sexual orientation and gender identity within a developmental perspective are presented to aid in understanding sexual and gender identity formation. The unique pathways for sexual and gender expansive youth into the child welfare system are discussed, underscoring the cumulative effects of past traumas they have experienced in their homes, schools, communities, and from within the foster care system itself. Child welfare policies and protections, along with the need for advocacy, are outlined. Best practices are presented as a critical intervention strategy to ensure positive outcomes related to the health, well-being, education, and permanence for youth. Educational, supportive, and networking resources are provided for sexual and gender expansive youth, professionals, foster and adoptive parents, and scholars.