The idea of withdrawal from secular society was central to the notions of monasticism and monastic architecture. The word derives from μόνος (mónos, Greek for ‘alone’). Christian monasticism made its first traceable appearances at the end of the 3rd century in Egypt and Palestine, though we know little of its architecture at this early stage. The eremitic ideal of the solitary saint retained its appeal, but was soon complemented by cenobitic monasticism where likeminded male or female ascetics joined together in communities that built architecture that was used in common. Monasticism as a religious form of life is found in Buddhism, Islam, and other traditions, though this essay will emphasize the medieval West, where monasteries were popular beginning in the 5th century. The various orders or congregations formulated differing architectural responses to their needs. The 9th-century Plan of Saint Gall, for example, represents an ideal meant to inspire emulation. Some monasteries were designed only for their resident populations of monks or nuns, while others might accommodate lay brothers or sisters, serfs, parish communities, visiting pilgrims, or dignitaries. A number of cathedrals across Europe were in fact monastic, following most often the Augustinian rule. The cenobitic monastery typically provided spaces for worship (church), sleeping (dormitory), dining (refectory), and meeting (chapter house) for the resident community, as well as buildings for reception and accommodation of visitors and other more functional structures (stables, storage barns, forges, mills, etc.). Monastic communities varied in size and might be very small or quite large. Some were found near or within urban locations, while others commanded large agricultural lands, including dependent parishes and granges. A survey of monastic architecture must therefore include industrial and hydraulic structures such as mills and dams, storage structures such as barns, dependent priory and farm buildings, and buildings for the care of the sick and infirm. Bibliography on monastic architecture is often divided regionally, and often focuses upon the church rather than the entire complex. Scholarship has privileged the architecture of certain orders—Cluniac Benedictines, Cistercians, and Franciscans, for example—over the more than five hundred monastic orders and congregations that once existed during the European Middle Ages. Archival research, architectural analysis, and archaeology are all contributing to a broader picture of the range and diversity of monastic architecture for male, female, and double houses. Traditional approaches to medieval architecture and its decoration have been primarily formalist, anchoring stylistic observations upon church records read as building documents in order to establish chronologies. While this approach remains important, new approaches such as stone-for-stone recording, C-14 dating of lime mortar and plaster, and dendrochronology, as well as the scientific study of painted layers and 3D modeling, are reshaping the history of medieval buildings. Together with archaeological analysis, early-21st-century work is examining the longer and more complicated cultural biographies of buildings and sites. This more integrated approach has recognized that architecture is not merely a reflection of monastic reform, but rather plays a strategic role in shaping it.