This chapter from School Mental Health Services for Adolescents provides an overview of the professionals most often at the forefront of school mental health service delivery, including teachers, school counselors, school psychologists, school social workers, and school nurses. It explores the training these professionals typically receive, as outlined by the relevant professional accrediting bodies, and discusses the roles these professionals assume in schools. The chapter also explores how those roles have evolved in recent years in relation to expanded school mental health (ESMH) efforts. It is clear that school mental health practitioners have training comparable to their community-based counterparts, but this capability is routinely underutilized in practice.