The 2007 Abel Symposium took place at the University of Oslo in August 2007.  The goal of the symposium was to bring together mathematicians whose research efforts have led to recent advances in algebraic geometry, algebraic K-theory, algebraic topology, and mathematical physics.  A common theme of this symposium was the development of new perspectives and new constructions with a categorical flavor.  As the lectures at the symposium and the papers of this volume demonstrate, these perspectives and constructions have enabled a broadening of vistas, a synergy between once-differentiated subjects, and solutions to mathematical problems both old and new.