Automorphic forms are one of the central topics of analytic number theory. In fact, they sit at the confluence of analysis, algebra, geometry, and number theory. In this book, Henryk Iwaniec once again displays his penetrating insight, powerful analytic techniques, and lucid writing style. The first edition of this volume was an underground classic, both as a textbook and as a respected source for results, ideas, and references. The book's reputation sparked a growing interest in the mathematical community to bring it back into print. The AMS has answered that call with the publication of this second edition. In the book, Iwaniec treats the spectral theory of automorphic forms as the study of the space \(L^2 (H\Gamma)\), where \(H\) is the upper halfplane and \(\Gamma\) is a discrete subgroup of volumepreserving transformations of \(H\). He combines various techniques from analytic number theory. Among the topics discussed are Eisenstein series, estimates for Fourier coefficients of automorphic forms, the theory of Kloosterman sums, the Selberg trace formula, and the theory of small eigenvalues. Henryk Iwaniec was awarded the 2002 AMS Cole Prize for his fundamental contributions to analytic number theory. Also available from the AMS by H. Iwaniec is Topics in Classical Automorphic Forms, Volume 17 in the Graduate Studies in Mathematics series. The book is designed for graduate students and researchers working in analytic number theory. This book is copublished by the AMS and Revista Matemática Iberoamericana (RMI), Madrid, Spain. Readership Graduate students and researchers working in analytic number theory. Reviews "Offers a swift introduction ... The material and the exposition are well suited for use by undergraduate students. Researchers from other fields and graduate students entering the field will also benefit from this wellwritten book ... comprehensive book ... highly recommend it to students and researchers who are interested in number theory."  Bulletin of the LMS From a review of the first edition: "The material and exposition are wellsuited for secondyear or higher graduate students ... This clear and comprehensive book concerning the spectral theory of \(\mathrm{GL} (2)\) automorphic forms belongs on many a bookshelf."  Mathematical Reviews "Gives a superb introduction to real analytic automorphic forms and their applications in number theory starting at a modest level and leading up to topics of current research ... book belongs in any institutional library. If you did not succeed in buying your copy of the first edition hurry up and order your copy of this one."  Zentralblatt MATH Table of Contents  Introduction
 Harmonic analysis on the Euclidean plane
 Harmonic analysis on the hyperbolic plane
 Fuchsian groups
 Automorphic forms
 The spectral theorem. Discrete part
 The automorphic Green function
 Analytic continuation of the Eisenstein series
 The spectral theorem. Continuous part
 Estimates for the Fourier coefficients of Maass forms
 Spectral theory of Kloosterman sums
 The trace formula
 The distribution of eigenvalues
 Hyperbolic latticepoint problems
 Spectral bounds for cusp forms
 Classical analysis
 Special functions
 References
 Subject index
 Notation index
