All central concepts in philosophy contain a relational aspect. The type of reality to be accorded to relations is for this reason one of the core questions of philosophical thought. This is particularly so in the case of nominalism. This book is devoted to John Buridan. While his towering importance in the late Middle Ages and for the development of early modern science has been recognised, his works are still not really well known. How does his theory of relations relate to those of his contemporaries, for example William of Ockham or Gregory of Rimini? The question of the reality of relations is not only of interest as an "experimentum crucis" of nominalism, but also because Buridan in his ethics frequently falls back upon older traditions. The first part of the book contains a discussion of theories of relation from Thomas Aquinas to Gregory of Rimini. The author then offers an exhaustive presentation of the basic lines of Buridan's philosophy and its relation to theology, before turning attention to his theory of relation. Finally he addresses particular forms of relation (identity, analogy, causality, etc.).