This is the first of two volumes containing papers submitted by the invited speakers to the 11th International Congress of Logic, Methodology and Philosophy of Science, held in Cracow in 1999, under the auspices of the International Union of History and Philosophy of Science, Division of Logic, Methodology and Philosophy of Science. The invited speakers are the leading researchers and accordingly the book presents the current state of the intellectual discourse in the respective fields. The papers delivered at the congress were divided into 17 sections. Thus the structure of the volume corresponds to the very schedule of the congress. Volume one contains the opening lecture by Andrzej K. Wroblewski as well as invited papers in sections of Proof Theory, Model Theory, Recursion Theory, Axiomatic Set Theory, Logic and Computation, Logic, Language and Cognition, Methodology, Probability, Induction, and Decision Theory, Philosophy of Logic, Mathematics, and Computer Science, and Philosophy of the Physical Sciences.