This chapter describes the vulnerable populations most often encountered by psychiatric-mental health nurses (PMHN). It addresses the major mental health issues commonly involved and the nurse’s role when working with each of these populations. The chapter explores the specialty practice of forensic nursing, and describes the requirements for practice and the forensic nurse’s roles and functions. In the emergency or trauma setting, forensic nurses work with victims of automobile accidents, suicide attempts, disasters, work-related injuries, and traumatic injuries. In the area of interpersonal violence, the forensic nurse may work with victims of domestic violence or sexual assault, child or elder abuse, human trafficking, and physical or psychological abuse. In patient-care facilities such as hospitals or nursing homes, they may help investigate accidents, injury, neglect, and inappropriate medication or other treatments.