In United States and Canadian law, competence concerns the mental capacity of an individual to participate in legal proceedings or transactions, and the mental condition a person must have to be responsible for his or her decisions or acts. Competence is an attribute that is decision-specific. Depending on various factors which typically revolve around mental function integrity, an individual may or may not be competent to make a particular medical decision, a particular contractual agreement, to execute an effective deed to real property, or to execute a will having certain terms.

Depending on the state, a guardian or conservator may be appointed by a court for a person who satisfies the state's tests for general incompetence, and the guardian or conservator exercises the incompetent's rights for the incompetent. Defendants who do not possess sufficient "competence" are usually excluded from criminal prosecution, while witnesses found not to possess requisite competence cannot testify. The English equivalent is fitness to plead.