This book based on lectures given by James Arthur discussesthe trace formula of Selberg and Arthur. The emphasis islaid on Arthur's trace formula for GL(r), with severalexamples in order to illustrate the basic concepts. The bookwill be useful and stimulating reading for graduate studentsin automorphic forms, analytic number theory, andnon-commutative harmonic analysis, as well as researchers inthese fields. Contents:I. Number Theory and Automorphic Representations.1.1. Someproblems in classical number theory, 1.2. Modular forms andautomorphic representations; II. Selberg's Trace Formula2.1. Historical Remarks, 2.2. Orbital integrals andSelberg's trace formula, 2.3.Three examples, 2.4. Anecessary condition, 2.5. Generalizations and applications;III. Kernel Functions and the Convergence Theorem, 3.1.Preliminaries on GL(r), 3.2. Combinatorics and reductiontheory, 3.3. The convergence theorem; IV. The Ad lic Theory,4.1. Basic facts; V. The Geometric Theory, 5.1. The JTO(f)and JT(f) distributions, 5.2. A geometric I-function, 5.3.The weight functions; VI. The Geometric Expansionof theTrace Formula, 6.1. Weighted orbital integrals, 6.2. Theunipotent distribution; VII. The Spectral Theory, 7.1. Areview of the Eisenstein series, 7.2. Cusp forms,truncation, the trace formula; VIII.The Invariant TraceFormula and its Applications, 8.1. The invariant traceformula for GL(r), 8.2. Applications and remarks