This book is a translation of the earlier book written by Koji Doi and the author, who revised it substantially for this English edition. It offers the basic knowledge of elliptic modular forms necessary to understand recent developments in number theory. It also treats the unit groups of quaternion algebras, rarely dealt with in books; and in the last chapter, Eisenstein series with parameter are discussed following the recent work of Shimura.
Another classic in the theory of modular forms with a unique approach to the theory from a geometric point of view. The geometric treatment of moduli spaces is definitely one of the best in any book on the theory of modular forms. The book focuses on Eisenstein series on subgroups and mainly those of low weights mainly weights 1 and 2. It is considered a hard book for beginners in the theory of modular forms but the treatment is definitely elegant.