The authors are internationally recognized experts in the object-oriented software field. Dr. Erich Gamma is technical director at the Software Technology Center of Object Technology International in Zurich, Switzerland. Dr. Richard Helm is a member of the Object Technology Practice Group in the IBM Consulting Group in Sydney, Australia. Dr. Ralph Johnson is a faculty member at the University of Illinois at Urbana-Champaign's Computer Science Department. Dr. John Vlissides conducts his research at IBM's Thomas J. Watson Research Center in Hawthorne, New York.