John Lydford was a fourteenth-century canon lawyer and cleric who acted as an advocate in the church court at Canterbury and held various official positions in the English church. He left a book of notes and documents relating tocanon law, which are edited here with an introduction. Its contents include legal formulas for use in court cases, notes about points of law, and records of particular cases drawn from the church courts of Oxford, Hereford, Winchester and Exeter. John Lydford's book therefore offers an unusual insight into the workings of the medieval English church and its courts.