'The book is beautifully written with an attractive style of presenting main results then discussing variants immediately in a smaller typeface. The exposition is precise and succinct, yet enough detail is provided for main proofs to be verified. Thus the book will appeal to the student as much as to the specialist. With the importance of the subject to classical analysis as well as to the various fields of application, it seems destined to become a classic. Students in need of inspiration for problems will find plenty here as well.' Mathematical Reviews