• 2009 C.I.M.E. Summer Course, Cetraro Italy. Summer School on Regularity of Degenerate Parabolic Equations
• 2005 Cortona Italy, Summer School on Harnack Inequalities and Positivity
• 1997 University of Rome, Tor Vergata, Italy;
• 1994 University of Cantabria, Santander, Spain;
• 1993 Korean National Univ. Seoul, Korea;
• 1992 Summer School of Mathematics, Universidad Complutense de Madrid, Spain;
• 1990 Lipschitz lectures Institute f"ur Angewandte Mathematik, Bonn, Germany;
• 1989 University of Beijing People Rep. of China;
• 1988 Instituto Alta Matematica F. Severi, Rome Italy;
• 1986 International Institute for Theoretical Physics, Trieste Italy.