A nurse who is responsible for total health care of a person must take care of both physical and emotional needs; therefore she should develop a basic understanding and skill in psychiatric nursing. This chapter focuses on general principles and standards of mental health nursing, psychiatric nursing skills and conceptual models. It also highlights signs and symptoms of mental illnesses, classification of mental disorders, review of personality development, defense mechanisms, maladaptive behavior, etiology of mental illnesses, structure and functions of brain and limbic system.