The chapter talks about mental health nursing or psychiatric nursing. Mental health is a state of balance between the individual and the surrounding world, a state of harmony between oneself and others, a coexistence between the realities of the self and that of other people and the environment. Mental illness produces a disharmony in the person’s ability to meet human needs comfortably or effectively and function within a culture. A multidisciplinary approach refers to collaboration between psychiatrist, psychiatric nurse, clinical psychologist, psychiatric social worker, occupational therapist or an activity therapist, and counselor. World Health Organization’s classification of mental disorders like ICDlO (International Statistical Classification of Disease and Related Health Problems)-1992 are also stated. Professional practice standards in mental health nursing and general principles of psychiatric nursing are discussed. Other topics included in the chapter are concepts of personality development, the therapeutic nurse-patient relationship, the individual with functional psychiatric disorder, classification of organic mental disorders, organic amnestic syndrome, childhood psychiatric disorders, therapeutic modalities in psychiatry, and legal aspects of mental health nursing.