Forensic psychiatry is a sub-speciality of psychiatry

Psychiatry

Psychiatry is the medical specialty devoted to the study and treatment of mental disorders. These mental disorders include various affective, behavioural, cognitive and perceptual abnormalities...

 and an auxiliar science of criminology

Criminology

Criminology is the scientific study of the nature, extent, causes, and control of criminal behavior in both the individual and in society...

. It encompasses the interface between law

Law

Law is a system of rules and guidelines which are enforced through social institutions to govern behavior, wherever possible. It shapes politics, economics and society in numerous ways and serves as a social mediator of relations between people. Contract law regulates everything from buying a bus...

 and psychiatry. A forensic psychiatrist provides services – such as determination of competency to stand trial – to a court of law to facilitate the adjudicative process.
Forensic psychiatrists work with court

Court

A court is a form of tribunal, often a governmental institution, with the authority to adjudicate legal disputes between parties and carry out the administration of justice in civil, criminal, and administrative matters in accordance with the rule of law...

s evaluating an individual's competency to stand trial

Trial (law)

In law, a trial is when parties to a dispute come together to present information in a tribunal, a formal setting with the authority to adjudicate claims or disputes. One form of tribunal is a court...

, defences based on mental diseases or defects (e.g., the "insanity" defense), and sentencing

Sentence (law)

In law, a sentence forms the final explicit act of a judge-ruled process, and also the symbolic principal act connected to his function. The sentence can generally involve a decree of imprisonment, a fine and/or other punishments against a defendant convicted of a crime...

 recommendations.