ILYA PRIGOGINE is Director of the Instituts Internationaux dePhysique et de Chimie, E. Solvay, Brussels, Belgium. Dr. Prigogineis also the Ashbel Smith Professor of Physics at The University ofTexas at Austin, where he is also Director of the Ilya PrigogineCenter for Studies in Statistical Mechanics and Complex Systems. In1977 he was awarded the Nobel Prize in Chemistry. STUART A. RICE is the Frank P. Hixon Distinguished ServiceProfessor in the James Franck Institute and the Department ofChemistry of the University of Chicago.