Three quarters of countries around the world have mental health legislation. Compulsory admission to mental health facilities (also known as Involuntary commitment or sectioning), is a controversial topic. From some points of view it can impinge on personal liberty and the right to choose, and carry the risk of abuse for political, social and other reasons; from other points of view, it can potentially prevent harm to self and others, and assist some people in attaining their right to healthcare when unable to decide in their own interests.

All human-rights oriented mental health laws require proof of the presence of a mental disorder as defined by internationally accepted standards, but the type and severity of disorder that counts can vary in different jurisdictions. The two most often utilized grounds for involuntary admission are said to be serious likelihood of immediate or imminent danger to self or others, and the need for treatment. Applications for someone to be involuntarily admitted may usually come from a mental health practitioner, a family member, a close relative, or a guardian. Human-rights-oriented laws usually stipulate that independent medical practitioners or other accredited mental health practitioners must examine the patient separately and that there should be regular, time-bound review by an independent review body. An individual must be shown to lack the capacity to give or withhold informed consent (i.e. to understand treatment information and its implications). Proxy consent (also known as substituted decision-making) may be given to a personal representative, a family member or a legally appointed guardian, or patients may have been able to enact an advance directive as to how they wish to be treated. The right to supported decision-making may also be included in legislation. Involuntary treatment laws are increasingly extended to those living in the community, for example outpatient commitment laws (known by different names) are used in New Zealand, Australia, United Kingdom and most of the United States.

The World Health Organization reports that in many instances national mental health legislation takes away the rights of persons with mental disorders rather than protecting rights, and is often outdated. In 1991, the United Nations adopted the Principles for the Protection of Persons with Mental Illness and the Improvement of Mental Health Care, which established minimum human rights standards of practice in the mental health field. In 2006 the UN formally agreed the Convention on the Rights of Persons with Disabilities to protect and enhance the rights and opportunities of disabled people, including those with psychosocial disabilities

The term insanity, sometimes used colloquially as a synonym for mental illness, is often used technically as a legal term.