Psychiatry is the medical specialty devoted to the study and treatment of mental disorders—which include various affective, behavioural, cognitive and perceptual disorders. The term was first coined by the German physician Johann Christian Reil in 1808. It literally means the 'medical treatment of the mind' (psych-: mind; -iatry: medical treatment; from Greek iātrikos: medical, iāsthai: to heal). A medical doctor specializing in psychiatry is a psychiatrist.

Mental disorders are currently conceptualized as disorders of brain circuits likely caused by developmental processes shaped by a complex interplay of genetics and experience. In other words, the genetics of mental illness may really be the genetics of brain development, with different outcomes possible, depending on the biological and environmental context.

Psychiatric assessment typically starts with a mental status examination and the compilation of a case history. Psychological tests and physical examinations may be conducted, including on occasion the use of neuroimaging or other neurophysiological techniques. Mental disorders are diagnosed in accordance with criteria listed in diagnostic manuals such as the widely used Diagnostic and Statistical Manual of Mental Disorders (DSM), published by the American Psychiatric Association, and the International Classification of Diseases (ICD) edited and used by the World Health Organization. The 5th edition of the DSM (DSM-5) is scheduled to be published in 2013, and is expected to have significant impact on many medical fields.

Psychiatric treatment applies a variety of modalities, including medication, psychotherapy and a wide range of other techniques such as transcranial magnetic stimulation. Treatment may be as an inpatient or outpatient, according to severity of function impairment/the disorder in question. Research and treatment within psychiatry as a whole are conducted on an interdisciplinary basis, sourcing an array of sub-specialties and theoretical approaches.

Philip Campbell, the Editor of the journal Nature, has dubbed the 10-year period of 2010-2019 to be the "decade for psychiatric disorders," referring to the point that research on mental illness has, at long last, reached an inflection point at which insights gained from genetics and neuroscience would transform the understanding of psychiatric illnesses. The Journal of the American Medical Association (JAMA) has also devoted its May 19, 2010 issue to the theme of mental health, testifying to the central importance of mental disorders and mental health in medical practice.
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While the medical specialty of psychiatry utilizes research in the field of neuroscience, psychology, medicine, biology, biochemistry, and pharmacology, it has generally been considered a middle ground between neurology and psychology. Unlike other physicians and neurologists, psychiatrists specialize in the doctor-patient relationship and are trained to varying extents in the use of psychotherapy and other therapeutic communication techniques. Psychiatrists also differ from psychologists in that they are physicians and the entirety of their post-graduate training is revolved around the field of medicine. Psychiatrists can therefore counsel patients, prescribe medication, order laboratory tests, utilize neuroimaging in a research setting, and conduct physical examinations.
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