For seventeen troubled years between the two world wars the Church was led by one of the most remarkable Popes of modern times. Pius XI's personal gifts were many, his activities as varied as the problems he labored to solve. The heart of his thought and the dynamism of his leadership are found in the great body of encyclicals he issued -a legacy of wisdom mankind will be drawing on for centuries. There is scarcely a problem disturbing the world today that is not illumined by the teaching of this great Pontiff. Thoroughly, definitively these extraordinary documents cover peace, marriage, education, the priesthood, the role of the laity in the Church, social justice, the state and man's relation to it - all the burning issues of our century. Though he spoke primarily as head of the Catholic Church, his words express the noblest aspirations of all men of good will.