Starting with the Council of Trent (1545-1563), the Church showed a great attention to the formation of the future priests. During the years, the popes gave a lot of indications to improve the modalities of formation, conforming to the pastoral milieu and the social conditions of the candidates. In 1965, at 28 October, the counciliar Fathers voted the decree Optatam totius. This document continues harmoniously the traditional principles of the seminarian formation, through the natural opening toward the legitimate exigency of this new time. In this article is presented the content of this decree which renovated the life in the seminaries and all the formation’s areas.