An apostolic constitution (Latin: constitutio apostolica) is the most solemn form of legislation issued by the Pope. The use of the term constitution comes from Latin constitutio, which referred to any important law issued by the Roman emperor, and is retained in church documents because of the inheritance that the canon law of the Roman Catholic Church received from Roman law.

By their nature, apostolic constitutions are addressed to the public. Generic constitutions use the title apostolic constitution and treat on solemn matters of the church, such as the promulgation of laws or definitive teachings. The forms dogmatic constitution and pastoral constitution are titles sometimes used to be more descriptive as to the document's purpose.

Apostolic constitutions are issued as papal bulls because of their solemn, public form. Among types of papal legislation, apostolic letters issued motu proprio are next in solemnity.