This volume contains the proceedings of the fourth International Joint Conference on the Theory and Practice of Software Development, TAPSOFT '93. Since the first in 1985, the aim of these conferences has been to bring together theoretical computer scientists and researchers in software engineering with a view to discussing how formal methods can usefully be applied in software development. TAPSOFT '93 consists ofthree parts: an advanced seminar, the Colloquium on Trees in Algebra and Programming (CAAP), and the Colloquium on Formal Approaches of Software Engineering (FASE). The advanced seminar includes four invited surveys and four invited conferences. The selected papers for CAAP are organized in seven sessions: specifications and proofs, concurrency, automata and counting, constraints solving, rewriting, logic and trees, analysis of algorithms, and a common session with FASE on type inference. The selected papers for FASE are presented in eight sessions: case studies in formal design and development, compositionality modules and development, formal development, foundations and analysis of formal specifications, verification of concurrent systems, model checking, parallel calculus, and a common session with CAAP on type inference.