This book consitutes the refereed proceedings of the 4th International Conference on Mathematics of Program Construction, MPC'98, held in Marstrand, near Goteborg, Sweden, in June 1998. The 17 revised full papers presented were selected from 57 submissions; also included are three invited contributions. The volume is devoted to the use of crisp, clear mathematics in the discovery and design of algorithms and in the development of corresponding software and hardware; varoius approaches to formal methods for systems design and analysis are covered.