Consent occurs when one person voluntarily agrees to the proposal or desires of another. It is a term of common speech, with specific definitions used in such fields as the law, medicine, research, and sexual consent. Consent as understood in specific contexts may differ from its everyday meaning. For example, a person with a mental disorder, a low mental age, or under the legal age of sexual consent may willingly engage in a sexual act that still fails to meet the legal threshold for consent as defined by applicable law.

United Nations agencies and initiatives in sex education programs believe that teaching the topic of consent as part of a comprehensive sexuality education is beneficial. Types of consent include implied consent, express consent, informed consent and unanimous consent.

The concept of end-user given consent plays an important role in digital regulations such as the European General Data Protection Regulation (GDPR). The GDPR (Article 6) defines a set of different legal bases for lawful processing of personal data. End-users' consent is only one of these possible bases. However, as a result of the GDPR enforcement (in 2018) and other legal obligations, data controllers (online service providers) have widely developed consent-obtaining mechanisms in recent years. According to the GDPR, end-users' consent should be valid, freely given, specific, informed and active. But the lack of enforceability regarding obtaining lawful consents has been a challenge in the digital world. As an example, a 2020 study, showed that the Big Tech, i.e. Google, Amazon, Facebook, Apple, and Microsoft (GAFAM), use dark patterns in their consent obtaining mechanisms, which raises doubts regarding the lawfulness of the obtained consent.

Consent can be either expressed or implied. For example, participation in a contact sport usually implies consent to a degree of contact with other participants, implicitly agreed and often defined by the rules of the sport. Another specific example is where a boxer cannot complain of being punched on the nose by an opponent; implied consent will be valid where the violence is ordinarily and reasonably to be contemplated as incidental to the sport in question. Express consent exists when there is oral or written agreement, particularly in a contract. For example, businesses may require that persons sign a waiver (called a liability waiver) acknowledging and accepting the hazards of an activity. This proves express consent, and prevents the person from filing a tort lawsuit for unauthorised actions.^{[citation needed]}

In English law, the principle of volenti non fit injuria (Latin: "to a willing person, injury is not done") applies not only to participants in sport, but also to spectators and to any others who willingly engage in activities where there is a risk of injury. Consent has also been used as a defense in cases involving accidental deaths during sex, which occur during sexual bondage. Time (May 23, 1988) referred to this latter example, as the "rough-sex defense". It is not effective in English law in cases of serious injury or death.

As a term of jurisprudence prior provision of consent signifies a possible defence (an excuse or justification) against civil or criminal liability. Defendants who use this defense are arguing that they should not be held liable for a tort or a crime, since the actions in question took place with the plaintiff or "victim's" prior consent and permission.^{[citation needed]}

In medical law, consent is important to protect a medical practitioner from liability for harm to a patient arising from a procedure. There are exemptions, such as when the patient is unable to give consent.

Also, a medical practitioner must explain the significant risks of a procedure or medication (those that might change the patient's mind about whether or not to proceed with the treatment) before the patient can give a binding consent. This was explored in Australia in Rogers v Whitaker. If a practitioner does not explain a material risk that subsequently eventuates, then that is considered negligent. These material risks include the loss of chance of a better result if a more experienced surgeon had performed the procedure. In the UK, a Supreme Court judgment modernized the law on consent and introduced a patient-focused test to UK law: allowing the patient rather than the medical professionals to decide upon the level of risk they wish to take in terms of a particular course of action, given all the information available. This change reflects the Guidance of the General Medical Council on the requirement to consent patients, and removes the rule of medical paternalism.