This volume is the Proceedings of Logic Colloquium 90 held in Helsinki, Finland, from July 15 to July 22, 1990. The congress belongs to the annual series of the European Summer Meetings of the Association for Symbolic Logic. These proceedings contain 13 research papers written mainly by the invited speakers of the congress. They represent all fields of mathematical logic from the philosophy of mathematics through model theory, proof theory, recursion theory and set theory, to connections of logic to computer science.