This volume studies the development of the theory of the relations of Church and State as found in the writings of a leading American Roman Catholic theologian, John Courtney Murray. Writings of Msgr. Murray for the period, 1942-1954, are drawn upon as chief sources. The writer identifies three focal points in his subject's theory: the freedom of the church; the harmony of laws with the church's teaching; and co-operation between church and state in matters of mutual importance. Christian man is described in his dual nature as Christian and as Citizen. the liberal spirit of Ma. Murray's has not always been received favorably by conservative forces in the church, and the account of this tension is reviewed by the author. The book has traits that suggest its origin in a doctoral dissertation. Nevertheless, the style is clear and the development orderly; and the discussion makes a real contribution to the current interest in church- state relationships.