In 1938, at the Institute for Advanced Study, E Hecke gave a series of lectures on his theory of correspondence between modular forms and Dirichlet series. Since then, the Hecke correspondence has remained an active feature of number theory and, indeed, it is more important today than it was in 1936 when Hecke published his original papers.This book is an amplified and up-to-date version of the former author's lectures at the University of Illinois at Urbana-Champaign, based on Hecke's notes. Providing many details omitted from Hecke's notes, it includes various new and important developments in recent years. In particular, several generalizations and analogues of the original Hecke theory are briefly described in this concise volume.
The book presents the Hecke correspondence theory in great generality on Hecke groups. I believe it is the only book in the market that gives the correspondence theory besides Hecke's original book which is out of print. Hecke correspondence is one of the main motivations for the theory of modular forms and the relations between modular forms and L-functions. Basically one relates modular forms to L-functions via functional equations. A must-have reference book.