Psychopathology is the study of mental illness. It includes the signs and symptoms of all mental disorders. The field includes abnormal cognition, maladaptive behavior, and experiences which differ according to social norms. This discipline is an in-depth look into symptoms, behaviors, causes, course, development, categorization, treatments, strategies, and more.

Biological psychopathology is the study of the biological etiology of abnormal cognitions, behaviour and experiences. Child psychopathology is a specialization applied to children and adolescents.

Early explanations for mental illnesses were influenced by religious belief and superstition. Psychological conditions that are now classified as mental disorders were initially attributed to possessions by evil spirits, demons, and the devil. This idea was widely accepted up until the sixteenth and seventeenth centuries.

The Greek physician Hippocrates was one of the first to reject the idea that mental disorders were the result of possession by demons or the devil, and instead looked to natural causes. He firmly believed the symptoms of mental disorders were due to diseases originating in the brain. Hippocrates suspected that these states of insanity were due to imbalances of fluids in the body. He identified four fluids in particular: blood, black bile, yellow bile, and phlegm. This later became the basis of the chemical imbalance theory used widely today.

Furthermore, not far from Hippocrates, the philosopher Plato would come to argue the mind, body, and spirit worked as a unit. Any imbalance brought to these compositions of the individual could bring distress or lack of harmony within the individual. This philosophical idea would remain in perspective until the seventeenth century. It was later challenged by Laing (1960) along with Laing and Esterson (1964) who noted that it was the family environment that led to the formation of adaptive strategies.

In the eighteenth century's Romantic Movement, the idea that healthy parent-child relationships provided sanity became a prominent idea. Philosopher Jean-Jacques Rousseau introduced the notion that trauma in childhood could have negative implications later in adulthood.

In the 1600s and 1700s insane asylums started to be opened to house those with mental disorders. Asylums were places where restraint techniques and treatments could be tested on patients who were confined. These were early precursors for psychiatric hospitals.

In 1875 the German book Textbook of Forensic Psychopathology was published, written by Richard von Krafft-Ebing, which became a standard psychiatric textbook for Universities across Germany.