This thesis examines the Carthusians in Great Britain and Ireland from an archaeological standpoint and highlights the role of the lay brother in the everyday life of the charterhouse. Using the case studies of Witham Charterhouse and Hinton Priory, the layouts of the lay brothers’ complexes are explored through geophysical survey and comparison with Carthusian material culture assemblages from other British charterhouses. This method of investigation provides a singular view of the lay brother in medieval society and for the first time proposes a layout of an English Carthusian lower house. The thesis begins with an introduction to the topic and gives an overview history of the Carthusians in Great Britain, before discussing in more detail areas of the charterhouse complex - the cell, church and cloister. Following this is a discussion of everyday life for the monks and lay brothers, exploring various facets including death and memory. The thesis then moves on to investigate the wider landscape of the monastery complex, and how the local area was exploited and utilised by the Carthusians. The monks’ and lay brothers’ interactions with secular society are considered through excavated assemblages from a number of charterhouses, which also demonstrates specific occupations for each of the inhabitants. The final chapter of the thesis presents the results of resistivity and magnetometer surveys at the two Somerset charterhouses and provides an interpretation of these results. It is concluded that it is not currently possible to identify the Carthusian lay brother as archaeologically distinct as there are not sufficient assemblages to provide an accurate understanding of the differences in monastic and lay objects. More research is therefore required before the lay brother can be properly understood.