This volume contains nine selected papers presented at the Borgholm conference. They were chosen on the basis of their immediate relevance to the most fundamental aspects of the theory of computation and the newest developments in this area. These papers, which have been extended and refereed, fall into eight categories: 1. Constructive Mathematics in Models of Computation and Programming; 2. Abstract Calculi and Denotational Semantics; 3. Theory of Machines, Computations and Languages; 4. Nondeterminism, Concurrency and Distributed Computing; 5. Abstract Algebras, Logics and Combinatorics in Computation Theory; 6. General Computability and Decidability; 7. Computational and Arithmetic Complexity; 8. Analysis of Algorithms and Feasible Computing.