William of Ockham's Summa Logicae (The Sum of Logic), composed in the mid-1320s, is a major work in the history of Western philosophy. It was highly influential for several centuries following its appearance. Ostensibly a textbook on logic, the work is an essential resource for understanding Ockham's philosophical project at large and contains numerous innovative ideas about thought, language, and ontology that are now attracting much interest in contemporary philosophy. Despite an abundant growth in Ockham scholarship in recent decades, this Critical Guide is the first collection of essays to be devoted to the Summa Logicae. The volume covers a wide range of topics, including nominalism, metalanguage, modes of signifying, Ockham's theory of the categorical syllogism, and modal logic. It provides both fresh perspectives on existing debates and new contributions on topics that have not yet entered mainstream scholarship on Ockham.