Harvard University, Fall semester, 1982

University of Pennsylvania, Winter 1983

Stanford University, Spring quarter, 1983

Visiting Fellow, University of California, Berkeley, Math Sciences Research Institute, January-March, 1986

Fellow Commoner, Churchill College, Cambridge, Cambridge University, April-June, 1986 and May-June 1987

École Polytechnique, Paris, July-August 1986

Stanford University, IMSSS, July-August 1987

Indira Gandhi Institute of Economic Development, Bombay, India, December 1987

KEPE, Research Institute of Greece, Athens, May 1988

University of Bonn, June 1988

Santa Fe Institute, Santa Fe, New Mexico, June 1989

Stanford University, IMSSS, August 1989

Kidder, Peabody & Co., February-July, 1990

Santa Fe Institute, January-June 1991

CORE, Université Catholique de Louvain, May 24-June 5, 1992

Hebrew University Third Jerusalem Summer School, June 15-24, 1992

Massachusetts Institute of Technology, Spring Semester 1996

Hebrew University, Eighth Jerusalem Summer School, June 16-25, 1997

Columbia University, Spring Semester 2002

Université Paris 1 Panthéon-Sorbonne, Fall 2004

Stanford University, SIEPR, Spring Semester 2011

Hebrew University Twenty-Second Jerusalem Summer School, June 15-24, 2011