A psychiatric hospital, also known as a mental health hospital, a behavioral health hospital, or an asylum is a specialized medical facility that focuses on the treatment of severe mental disorders. These institutions cater to patients with conditions such as schizophrenia, bipolar disorder, major depressive disorder, and eating disorders, among others.

Psychiatric hospitals vary considerably in size and classification. Some specialize in short-term or outpatient therapy for low-risk patients, while others provide long-term care for individuals requiring routine assistance or a controlled environment due to their psychiatric condition. Patients may choose voluntary commitment, but those deemed to pose a significant danger to themselves or others may be subject to involuntary commitment and treatment.

In general hospitals, psychiatric wards or units serve a similar purpose. Modern psychiatric hospitals have evolved from the older concept of lunatic asylums, shifting focus from mere containment and restraint to evidence-based treatments that aim to help patients function in society. Drug administration, as well as structured and one-to-one therapy (such as occupational therapy and psychotherapy) play a role in trajectories. They are the focus of most studies on forms of treatment that exist in psychiatric wards. However, because psychiatric wards are social living spaces, inpatient relationships in psychiatric wards also play a role in survival and recovery trajectories.

With successive waves of reform, and the introduction of effective evidence-based treatments, most modern psychiatric hospitals emphasize treatment, usually including a combination of psychiatric medications and psychotherapy, that assist patients in functioning in the outside world. Many countries have prohibited the use of physical restraints on patients, which includes tying psychiatric patients to their beds for days or even months at a time, though this practice still is periodically employed in the United States, India, Japan, and other countries.

Modern psychiatric hospitals evolved from, and eventually replaced, the older lunatic asylum. Their development also entails the rise of organized institutional psychiatry. Hospitals known as bimaristans were built in the Middle East in the early ninth century; the first was built in Baghdad under the leadership of Harun al-Rashid. While not devoted solely to patients with psychiatric disorders, early psychiatric hospitals often contained wards for patients exhibiting mania or other psychological distress.

Because of cultural taboos against refusing to care for one's family members, mentally ill patients would be surrendered to a bimaristan only if the patient demonstrated violence, incurable chronic illness, or some other extremely debilitating ailment. Psychological wards were typically enclosed by iron bars owing to the aggression of some of the patients.

In Western Europe, the first idea and set up for a proper mental hospital entered through Spain. A member of the Mercedarian Order named Juan Gilaberto Jofré traveled frequently to Islamic countries and observed several institutions that confined the insane. He proposed the founding of an institution exclusive for "sick people who had to be treated by doctors", something very modern for the time. The foundation was carried out in 1409 thanks to several wealthy men from Valencia who contributed funds for its completion. It was considered the first institution in the world at that time specialized in the treatment of mental illnesses.

Later on, physicians, including Philippe Pinel at Bicêtre Hospital in France and William Tuke at York Retreat in England, began to advocate for the viewing of mental illness as a disorder that required compassionate treatment that would aid in the rehabilitation of the victim. In the Western world, the arrival of institutionalisation as a solution to the problem of madness was very much an advent of the nineteenth century. The first public mental asylums were established in Britain; the passing of the County Asylums Act 1808 empowered magistrates to build rate-supported asylums in every county to house the many 'pauper lunatics'. Nine counties first applied, the first public asylum opening in 1812 in Nottinghamshire. In 1828, the newly appointed Commissioners in Lunacy were empowered to license and supervise private asylums. The Lunacy Act 1845 made the construction of asylums in every county compulsory with regular inspections on behalf of the Home Secretary, and required asylums to have written regulations and a resident physician.