Saint Vincent of Lérins was a Christian monk and theologian who lived in the 5th century. He is best known for his work, the Commonitorium, which outlines principles for distinguishing true Christian doctrine from heresy. His writings emphasize the importance of tradition and the consensus of the Church in understanding faith. Vincent is often associated with the Lérins Islands in France, where he spent much of his life. His ideas contributed to the development of the concept of Catholicity, which refers to the universality of the Church. He is commemorated in the liturgical calendar on April 24.