John Day was an English Protestant printer. He specialised in printing and distributing Protestant literature and pamphlets, and produced many small-format religious books, such as ABCs, sermons, and translations of psalms. He found fame, however, as the publisher of John Foxe's Actes and Monuments, also known as the Book of Martyrs, the largest and most technologically accomplished book printed in sixteenth-century England.

John Foxe was an English clergyman, theologian, and historian, notable for his martyrology Actes and Monuments, telling of Christian martyrs throughout Western history, but particularly the sufferings of English Protestants and proto-Protestants from the 14th century and in the reign of Mary I. The book was widely owned and read by English Puritans and helped to mould British opinion on the Catholic Church for several centuries.