The medieval Church had strict disciplinary rules about how Sunday should be observed, but in England there was considerable diversity in interpreting and honouring them. The medieval English Sunday is a vast and challenging subject, yet despite this, and the controversy excited by the Sunday Trading Act of 1994 which allowed shops to open, it has excited little recent attention.The discipline of Sunday was laid down in the Third Commandment (Exod. 20: 8–11), where Christians were ordered to keep holy the Sabbath day and told ‘In it thou shalt not do any work.’ This was reinforced in canon law, in episcopal mandates, in commentaries, in theological treatises, in sermons, in pastoralia, and in popular literature. The Sunday Christ, the image of Christ surrounded by craftsmen’s tools, which enshrined the idea that Sunday working with such implements crucified him anew, adorned the walls of many late medieval English parish churches. Secular rulers, starting with Wihtred of Kent (695), included Sabbath-keeping in their legislation. Diversity occurred in the varying interpretations of the law on Sunday observance, and in the patchiness of its enforcement. The questions to be addressed here are, firstly, what actually constituted Sunday? Secondly, what were people supposed to do on Sundays, and did they do it? Finally, how well observed was the work prohibition as applied to Sunday trading?