Paul Tillich is one of the theologians who has more clearly expressed what it means to be a Protestant. The Protestant principle and Protestantism are two concepts that have been present throughout his history as a Lutheran theologian, not only in his theological and phylosophical thought, but also in his biographical decisions. The protestant principle, understood as the justification by grace alone and the experience of the majesty of God in all spheres of life transcend protestantism, understanding it as a historical realization of the protestant principle. In this article Y try to present both concepts from the framework of the main reflection lines and vital experiences which are stated in the writings of Tillich.