Torture (from Latin tortus: to twist, to torment) is the act of deliberately inflicting severe physical or psychological suffering on someone by another as a punishment or in order to fulfill some desire of the torturer or force some action from the victim. Torture, by definition, is a knowing and intentional act; deeds which unknowingly or negligently inflict suffering or pain, without a specific intent to do so, are not typically considered torture.

Torture has been carried out or sanctioned by individuals, groups, and states throughout history from ancient times to modern day, and forms of torture can vary greatly in duration from only a few minutes to several days or longer. Reasons for torture can include punishment, revenge, extortion, persuasion, political re-education, deterrence, coercion of the victim or a third party, interrogation to extract information or a confession irrespective of whether it is false, or simply the sadistic gratification of those carrying out or observing the torture. Alternatively, some forms of torture are designed to inflict psychological pain or leave as little physical injury or evidence as possible while achieving the same psychological devastation. The torturer may or may not kill or injure the victim, but torture may result in a deliberate death and serves as a form of capital punishment. Depending on the aim, even a form of torture that is intentionally fatal may be prolonged to allow the victim to suffer as long as possible (such as half-hanging). In other cases, the torturer may be indifferent to the condition of the victim.

Although torture is sanctioned by some states, it is prohibited under international law and the domestic laws of most countries. Although widely illegal and reviled, there is an ongoing debate as to what exactly is and is not legally defined as torture. It is a serious violation of human rights, and is declared to be unacceptable (but not illegal) by Article 5 of the UN Universal Declaration of Human Rights. Signatories of the Geneva Conventions of 1949 and the Additional Protocols I and II of 8 June 1977 officially agree not to torture captured persons in armed conflicts, whether international or internal. Torture is also prohibited for the signatories of the United Nations Convention Against Torture, which has 163 state parties.

National and international legal prohibitions on torture derive from a consensus that torture and similar ill-treatment are immoral, as well as impractical, and information obtained by torture is far less reliable than that obtained by other techniques. Despite these findings and international conventions, organizations that monitor abuses of human rights (for example, Amnesty International, the International Rehabilitation Council for Torture Victims, Freedom from Torture, etc.) report widespread use condoned by states in many regions of the world. Amnesty International estimates that at least 81 world governments currently practice torture, some of them openly.