'This book is an important addition to the literature from authors who are leading experts in this field.' Glyn Harman, Bulletin of the London Mathematical Society '... carefully written, with an extensive bibliography, and will be of lasting value ...'. Thomas Ward, Zentralblatt fur Mathematik 'This book can be recommended not only to those interested in number-theoretic aspects, but also to those interests lie in topics related to dynamical systems ... self-contained and very readable.' EMS