HISTORIC BUILDING INVESTIGATIONS and selective excavations carried out during recent conservation works have shed new light on St Mary’s Guildhall, Boston (Lincolnshire), built by an internationally significant religious fraternity in one of the most important ports of medieval England. Dendrochronological dating of the guildhall indicates a construction date of c 1390. This is significantly earlier than had previously been supposed and suggests a close link between the construction of the guildhall and the grant of a royal licence of incorporation to the guild in 1392. It makes the guildhall one of the earliest securely dated brick buildings in Lincolnshire and is important evidence of investment during a period when Boston was experiencing severe economic decline. Multidisciplinary analysis of the archaeology of the building and some of the guild’s surviving documentary records enables a reconstruction of the original form and function of the guildhall and its now-lost material culture. Comparative analysis of Boston with other surviving provincial guildhalls begins to shed light on the emergence of a distinctive type of public architecture in pre-modern England.