A deep sense of unease permeates the physical sciences. We are in a time of great change: The end of the cold war has ushered in an era of shrinking budgets, painful restructuring and changing objectives. At the same time, the underlying assumptions of physics research have shifted. Traditionally, physics has been highly reductionist, analyzing nature in terms of smaller and smaller building blocks and revealing underlying, unifying fundamental laws. In the past this grand vision has bound the subdisciplines together. Now, however, the reductionist approach that has been the hallmark of theoretical physics in the 20th century is being superseded by the investigation of emergent phenomena, the study of the properties of complexes whose “elementary” constituents and their interactions are known. Physics, it could be said, is becoming like chemistry.