A quantitative description of biology is rapidly emerging as a major new frontier for science in the 21st century. This field involves the cross-fertilization of ideas and methods from biology and biochemistry on the one hand and the physics of complex systems on the other. Protein folding represents the premier case where this quantitative approach has been successful and is becoming an example for other fields in biology. Protein folding research is a multifaceted field of inquiry addressing fundamental problems in: polypeptide energetics and dynamics; chaperone-assisted structure formation; protein structure prediction; protein design; single-molecule detection; and the role of protein folding in diseases. The field has captured the interest of biologists, chemists, and physicists. Owing in part to technological and theoretical advances, protein-folding research has expanded dramatically during the past decade; the number of publications addressing protein folding has more than tripled since 1990. New measurement techniques have provided insights into the earliest steps in protein folding; theoretical work has led to the "new view" of protein folding based on energy landscape theory and the funnel concept; and misfolded proteins are emerging as significant factors in a number of diseases. Laboratories throughout the world are examining how proteins fold and misfold; critical advances in understanding these complex phenomena are emerging at an ever-increasing pace. In addition, theoretical and experimental collaborations are becoming responsible for major advances in this field. The Gordon Research Conference on Protein Folding Dynamics is becoming the main forum for discussion of these interactions.