  The purpose of this entry is to provide a systematic introduction to medieval views about the nature and ontological status of relations. Given the current state of our knowledge of medieval philosophy, especially with regard to relations, it is not possible to discuss all the nuances of even the best-known medieval philosophers’ views. In what follows, therefore, we shall restrict our aim to identifying and describing (a) the main types of position that were developed during the Middle Ages, and (b) the most important considerations that shaped their development. We shall have occasion along the way, however, to examine in detail certain aspects of the views of important representatives of all the main medieval positions, including Peter Abelard (1079–1142), Gilbert of Poitiers (1085–1154), Albert the Great (1200–1280), Thomas Aquinas (1225–1274), John Duns Scotus (1265–1308), Henry Harclay (1270–1317), Peter Auriol (1280–1322), and William Ockham (1285–1347).