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). (shrink)