This volume contains papers presented at the All-Union School on the Theory of Functions, held in Miass in July 1989. The papers examine topical trends in the theory of functions and their approximation. Among the topics included are extremal properties of functions, approximation and interpolation of functions by trigonometric polynomials and splines, widths of function classes, best approximation of operators, cubature formulas, and classical problems of analytic number theory.