Written in the course of his conversion to Catholicism, Newman’s “Essay on the Development of Christian Doctrine” ranks among the most decisive breakthroughs in systematic and historical theology of the modern era. Newman confronts the age-old problem, which he had wrestled with for his entire life, of how Christian doctrine can develop over time while retaining its roots in the original revelation of Christ. Newman first shows that constructive development is a natural, even predictable consequence of Christ’s investment of authority in the Church. He then provides clear, historically grounded criteria for distinguishing authentic developments from false novelties and fads. The result is a profound interpretation and defense of the Church’s mission and of its power to proclaim the whole counsel of God.