In 1922 Charles Hartshorne, then an aspiring young philosopher, wrote to Edgar Sheffield Brightman, a preeminent philosopher of religion for twenty-three subsequent years and, remarkably, almost every letter was preserved. In their introductory essays, editors Randall Auxier and Mark Davies place the unusually rich and intensive correspondence in its intellectual context and address the relationship between personalism and process philosophy/theology in metaphysics, epistemology, ethics, and social philosophy.