The Commonitorium is a theological work written by the early Christian theologian Vincent of Lérins in the 5th century. It addresses the importance of maintaining the integrity of Christian doctrine and tradition. Vincent emphasizes the need for a consensus among believers to safeguard the faith against heresies. In the Commonitorium, Vincent introduces the famous principle of "what has been believed everywhere, always, and by all" as a guideline for discerning authentic Christian teaching. This work has been influential in discussions about the development of doctrine within the Catholic Church and other Christian denominations.