The chapter provides an overview of the social, political, and economic functions of Byzantine monasteries from the ninth to the fifteenth century. Relations between monasteries and the state, the Church, and lay society were complex. The monks received donations and protection in exchange for various spiritual and material services. The great landowning monasteries engaged in large-scale agrarian production and trade, and they played a substantial role in local and regional economies. Finally, the chapter addresses the fate and significance of monasteries in the long period of crisis that began in the middle of the fourteenth century and ended with the replacement of the Byzantine by the Ottoman Empire.