Shortly after his conversion in 1929, C. S. Lewis wrote to a friend, “When all is said (and truly said) about the divisions of Christendom, there remains, by God’s mercy, an enormous common ground.” From that time on, Lewis thought that the best service he could do for his unbelieving neighbors was to explain and defend the belief that has been common to nearly all Christians at all times — that “enormous common ground” which he usually referred to as “mere” Christianity. Lewis’s defense of Christianity was colorfully varied — the subjects he covered ranged widely, including Christianity and literature, Christianity and culture, ethics, futility, church music, modern theology and biblical criticism, the Psalms, and petitionary prayer. Presented in chronological order, some of the fourteen papers included in this collection were written specifically for periodicals, while others, published here for the first time, were read to societies in and around Oxford and Cambridge. Common to them all, however, are the uniquely effective style of C. S. Lewis and the basic presuppositions of his theology — his “mere” Christianity.