TAPSOFT '89 is the Third International Joint Conference on Theory and Practice of Software Development held in Barcelona, Spain, March 13-17, 1989. The conference consisted of three parts: - Advanced Seminar on Foundations of Innovative Software Development - Colloquium on Trees in Algebra and Programming (CAAP '89) - Colloquium on Current Issues in Programming Languages (CCIPL) The TAPSOFT '89 Conference Proceedings are published in two volumes...