There has recently been a good deal of discussion of reasons in the philosophical literature, much of it motivated by the idea that the concept of a reason is basic to the normative realm, a fundamental concept in terms of which other normative notions can be analyzed. In this volume, John Horty brings to bear his work in logic to present a framework that allows for answers to key questions about reasons and reasoning, namely: What are reasons, and how do they support actions or conclusions? Given a collection of individual reasons, possibly suggesting conflicting actions or conclusions, how can we determine which course of action, or which conclusion, is supported by the collection as a whole? What is the mechanism of support? This book joins an important and active literature, but it also occupies a unique position. Most of the current work on reasons is concerned with a number of complex philosophical issues, such as, for example, the relation between reasons and motivation, desires, and values, the issue of internalism versus externalism in the theory of reasons, and the issue of objectivity versus subjectivity of reasons. Horty's book, by contrast, concentrates on developing a concrete theory of the way in which reasons might interact to support their outcomes. He brings to the study of reasons and their outcomes the same standards of rigor that Frege first applied in studying the relation between ordinary logical premises and their conclusions.