About the Author: ILYA PRIGOGINE is Director of the Instituts Internationaux de Physique et de Chimie, E. Solvay, Brussels, Belgium. Dr. Prigogine is also the Ashbel Smith Professor of Physics at The University of Texas at Austin, where he is also Director of the Ilya Prigogine Center for Studies in Statistical Mechanics and Complex Systems. In 1977 he was awarded the Nobel Prize in Chemistry. STUART A. RICE is the Frank P. Hixon Distinguished Service Professor in the James Franck Institute and the Department of Chemistry of the University of Chicago.