This Article identifies and analyzes a transsubstantive tool of constitutional doctrine that to date has escaped scholarly attention. The Article terms this device the “institution matching” canon. It can be stated briefly as follows: When the government makes a decision that may impinge upon a liberty or equality interest—which may or may not be directly judicially enforced otherwise—a court should determine whether the component of government that made the decision has actual competence in and responsibility for the policy justifications invoked to curtail the interest. If not, the court should reject the government action but leave open the possibility of a “do-over” by a more appropriate component of government. First identified in an early written opinion of Justice John Paul Stevens, the institution matching canon continues to play an important if imperfectly articulated role in criminal law, administrative law, and national security doctrine. This Article provides a systematic survey of the ways that the Court has employed institution matching and develops a taxonomy of the canon’s costs and benefits.