This volume constitutes the proceedings of the Third International Conference on the Mathematics of Program Construction, held at Kloster Irsee, Germany in July 1995. Besides five invited lectures by distinguished researchers there are presented 19 full revised papers selected from a total of 58 submissions. The general theme is the use of crisp, clear mathematics in the discovery and design of algorithms and in the development of corresponding software and hardware; among the topics addressed are program transformation, program analysis, program verification, as well as convincing case studies.