This book constitutes the refereed proceedings of the 24th Internation al Symposium on Mathematical Foundations of Computer Science, MFCSF99, held in Szklarska Poreba, Poland, in September 1999. The 37 revised full papers presented together with four invited contributions were ca refully selected from 68 submissions. The papers are organized in sect ions on computing over reals, compression techniques, foundations of p rogramming, complexity and algorithms, model checking, distributed com puting, functional programming, automata, security, logic, counting pr oblems, processes and bisimulation, graph algorithms, and type theory.