This volume contains papers selected for presentation at the 15th Symposium on Mathematical Foundations of Computer Science, MFCS '90, held at Banska Bystrica, Czechoslovakia, August 27-31, 1990. Previous MFCS proceedings have also been published in the Lecture Notes in Computer Science. This symposium is the 15th in a series of international meetings which have taken place in Czechoslovakia and Poland. The aim of these symposia is to bring together specialists in theoretical fields of computer science from various countries and to stimulate mathematical research in theoretical computer science. These proceedings consist of 10 invited papers and 52 communications selected by the international Program Committee. The papers present the latest results in key areas of computer science by authors from Europe, USA, Japan and China.