Dennis A Hejhal 
Selberg Trace Formula and Related Topics [PDF ebook] 

This volume provides both a good introduction to current work and a collection of survey articles on the Selberg trace formula and its applications. As the proceedings of a joint AMS-IMS-SIAM Summer Research Conference, this material represents a diverse set of attitudes toward the trace formula, including those from mathematical physics, classical analytic and modern adelic number theory, modern geometric representations, and classical harmonic analysis. The background required varies considerably, from introductory papers to those requiring familiarity with representation theory, the theory of automorphic forms, and number theory.