The conference on Proof Theory: History and Philosophical Significance held in 1997 at the University of Roskilde, Denmark, tracked the history of proof theory and its role in the analysis of the philosophical foundations of mathematics since Hilbert's original program to its modern, highly articulated form. This volume is a collection of papers presented at the conference. It can be read with profit and pleasure by philosophers, mathematicians, computer scientists and scholars with no professional training in proof theory, provided they have a general knowledge of foundational issues.