In a vigorous theological controversy, William Bishop, English Roman Catholic theologian educated at Oxford, Rheims, Rome, and Paris, took on William Perkins, the best-selling English Protestant writer of the late sixteenth and early seventeenth centuries. The two writers were formidable champions of their respective religious traditions. As I will argue, this was a significant exchange, though the dispute has been little noticed by historians of the period. The issues the two writers discussed and the way they discussed them throw considerable light on the state of English religion in the early seventeenth century. Bishop emerges as a more powerful and effective spokesman for the Roman Catholicism of his day than has been heretofore recognised.