The present edition differs from the original German one mainly in the following addi- tional material: weighted norm inequalities for maximal functions and singular opera- tors ( 12, Chap. XI), polysingular integral operators and pseudo-differential operators ( 7, 8, Chap. XII), and spline approximation methods for solving singular integral equations ( 4, Chap. XVII). Furthermore, we added two subsections on polynomial approximation methods for singular integral equations over an interval or with dis- continuous coefficients (Nos. 3.6 and 3.7, Chap. XVII). In many places we incorporated...