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 work is devoted to John Buridan. While his importance in the late Middle Ages and for the development of early modern science has been recognized, his works are still not very 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 this book contains a discussion of theories of relation from Thomas Aquinas to Gregory of Rimini. The author then offers a 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 (such as identity, analogy and causality).