This volume brings together papers from various fields of theoretical computer science, including computational geometry, parallel algorithms, algorithms on graphs, data structures and complexity of algorithms. Some of the invited papers include surveys of results in particular fields and some report original research, while all the contributed papers report original research. Most of the algorithms given are for parallel models of computation. The papers were presented at the Second International Symposium on Optimal Algorithms held in Varna, Bulgaria, in May/June 1989. The volume will be useful to researchers and students in theoretical computer science, especially in parallel computing.