Complexity theory has been a flourishing area of research in the last ten years and currently provides one of the most active subjects for future research problems in computer science. This volume provides a survey of the subject in the form of a collection of articles written by experts that to- gether provide a comprehensive guide to research. The editors' aim has been to provide an accessible description of the current state of complexity theory,and to demonstrate the breadth of techniques and results that make the subject exciting. Thus, papers run the gamut from sublogarithmic space to exponential time and from new combinatorial techniques to interactive proof systems. As a result, researchers in computer science will find this an excellent starting point for study in the subject and a useful source of the key results known.