The Clerks Regular of the Mother of God of Lucca are a Roman Catholic congregation of priests. The were founded by Saint Giovanni Leonardi, son of middle-class parents, who was born in 1541 at Diecimo, Republic of Lucca. He was ordained on December 22, 1572. It was not until 3 November 1621 that Gregory XV, carrying out what was always in the founder's mind, erected the congregation into a religious order proper by permitting its members to take solemn vows, and it henceforth became the Clerks Regular of the Mother of God.