Mental health practitioners can be traumatized in the line of duty, as when working with trauma survivors, and outside of their occupational roles, as members of the general population with its commensurate risks for crime, accidents, sexual violence, terrorism, or natural disasters. Research and clinical literature describes the effects of traumatization on practitioners, particularly regarding how it may affect the therapeutic relationship and treatment progress. In addition to providing descriptive and prescriptive information, the trauma literature reflects an increasing recognition of the need for skillful, informed supervision to support the well-being of clients and practitioners engaged in trauma work. This entry is intended to familiarize readers with the growing awareness and understanding of practitioner traumatization, its features, its effects on treatment, and guidelines for supervisors.