This volume contains 11 invited lectures and 42 communications presented at the 13th Conference on Mathematical Foundations of Computer Science, MFCS '88, held at Carlsbad, Czechoslovakia, August 29 - September 2, 1988. Most of the papers present material from the following four fields: - complexity theory, in particular structural complexity, - concurrency and parellelism, - formal language theory, - semantics. Other areas treated in the proceedings include functional programming, inductive syntactical synthesis, unification algorithms, relational databases and incremental attribute evaluation.