This book constitutes the refereed proceedings of the 24th International Symposium on Mathematical Foundations of Computer Science, MFCS'99, held in Szklarska Poreba, Poland, in September 1999. The 37 revised full papers presented together with four invited contributions were carefully selected from 68 submissions. The papers are organized in sections on computing over reals, compression techniques, foundations of programming, complexity and algorithms, model checking, distributed computing, functional programming, automata, security, logic, counting problems, processes and bisimulation, graph algorithms, and type theory.