The glorious heritage of cathedrals and castles in Europe today is the legacy of the medieval masons. The master mason, head of a team of masons, was the medieval equivalent to an architect. He acted as contractor, designer, and engineer, drawing up the plans, gathering the materials together, and erecting the building. He was responsible for the decoration as well, the capitals, bosses, and furnishings, but was also expected to turn his hand to any building work, however menial. With reference to masons' records, building contracts, and accounts, as well inscriptions, self-portraits, and personal marks, the author discusses who the masons were, how they organised their professional lives, the role of their patrons and how they designed and built the cathedrals and castles. Architectural drawings illustrate the skill involved and manuscript illuminations portray the masons at work, but the best evidence lies in the buildings themselves, the true testimony to their creative talents.