In a short introduction, the concept and history of logic in the Middle Ages is outlined. Then follow sections on the main concepts and theories, namely Terms, Properties of Terms, Sentences, Proofs of Sentences, Consequences, Insolubles, and Obligations. Some references to other articles on authors and notions are given. The Bibliography is divided, the Primary Sources contain medieval works on logic in English translation, the Secondary Sources list relevant monographs and collections. Finally, three references to internet sites are given.