A significant number of sources for the study of architectural practise survive from medieval Spanish kingdoms when compared to other European territories. Apprenticeship contracts, drawings, sketches and masons’ inventories shed light on the means by which architectural knowledge was transmitted in the Iberian peninsula between 1370 and 1450. This body of evidence – much of it newly discovered – also challenges many long-held assumptions, even if several key problems remain unresolved: the training requirements for masons’ apprentices, the specific skills that defined a master, or the role of drawing in the building process.