th The 13 Jerusalem Symposium on Quantum Chemistry and Bio- chemistry was dedicated to the memory of Ernst David Bergmann, one of the founders of this series of Symposia, at the occasion of the 5th anniversary of his death. The opening session was honored by the pre- sence of H. E. Yzhak Navon, President of the State of Israel and of Baron Edmond de Rothschild whose generous and constant support makes these Symposia possible. To both these distinguished guests we address the expression of our deep gratitude. Our thanks are also due to the Israel Academy of Sciences and Humanities, in particular to its President Professor Aryeh Dvoretzky and to the Hebrew University of Jerusalem for their hospita- lity and helpful association. I had the privilege this time to join efforts in the organi- zation of this Symposium with two distinguished American colleagues, Prof. P. O. P. Ts'o from Johns Hopkins University and Dr. Harry Gelboin from the National Institute for Cancer Research. I wish to thank them for their invaluable help and the two Institutions which they repre- sent for important financial support. th The subject of the 13 Jerusalem Symposium brings us back to that of the 1st Symposium held in 1967. The comparison of the two Proceedings enables us to evaluate the important developments which occurred in this field of research during the last 13 years.