The theory of automorphic forms is a cornerstone in modern number theory. It was an essential ingredient of the proof of Fermat's Last Theorem. However, in large part because of the lack of a suitable text this theory has been difficult for students to learn. This book addresses that difficulty. It begins with extensive foundational material and builds to topics on the resear ch frontier, such as the Langlands conjectures and the Weil representation.Researchers as well as students will find this a valuable guide to a notoriously difficult subject.