Psychopathology simply means the study of pathology of mind. It deals with disturbance of human behavior that occurs as a part of disorders of thought, emotion and perception and other cognitive functions. Review of structure and functions of brain are described to help the student nurse in better understanding of psychopathology. Neurotransmission is the process that allows the electrochemical transmission of nerve signals from one neuron to another at synapse. Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Etiology of abnormal behavior in psychiatric disorders is mentioned and predisposing, precipitating and perpetuating factors are given to be the cause of metal illnesses. Causes of mental illness are listed as biopsychosocial factors, psychological factors, and sociocultural factors. Two well-known and widely accepted systems in the classification of mental disorders, namely International Classification of Diseases (ICD) and Diagnostic and Statistical Manual (DSM) are well described. Signs and symptoms will be different in many psychiatric disorders, and sometimes many of the symptoms are overlapping among them. Knowledge about signs and symptoms of mental illness will be useful in assessment and provision of care.