After the 1563 Decree concerning Seminaries of the Council of Trent, each diocese was required to open a diocesan seminary. This article presents the foundation dates of Italian Tridentine diocesan seminaries and information concerning the procedure for opening such institutions. Since education was an integral part of the Catholic Reform, studying the educational institutions designed by that reform provides needed insight into the speed and effectiveness of the changes. Previous literature on seminaries falls into four categories: general, national, and local studies, and studies of seminaries run by religious orders. Much of this is commemorative, but late-twentieth-century diocesan and educational histories take a different and more practical approach to the institutions. The chart that follows the article demonstrates the relationship between councils and opening seminaries, identifies the most important seminary founders, and highlights areas of more intense educational reform.