The 14th Jerusalem Symposium continued the tradition of the pleasant and exciting meetings which once a year gather distinguished scientists, the world's most renowned experts in specific fields of quantum chemistry and biochemistry, in the impressive surroundings of the Israel Academy of Sciences and Humanities. The subject discussed this year - Intermolecular forces - is one of the utmost interest for all molecular sciences. I wish to thank all those who made this meeting possible and contributed toits success: the Baron Edmond de Rothschild whose continuous generosity guarantees the perenniality of our venture, t~e Israel Academy of Sciences and in particular its Vice-President, Pr~fes­ sor Yoshua Jortner for his devoted contribution to the organization and holding of this meeting, the high authorities of the Hebrew Uni­ versity of Jerusalem and in particular the Rector Meshulamfor their constant support and Dr. Pierre Claverie for his efficient help in the preparation of the program. Mrs Abigail Hyam and Mrs MyriamYogev must be thanked for their contribution to the efficiency and success of the local arrangements. Bernard Pullman ix B.Pullman[ed.},IntermolecularForces,ix. Copyright ©1981byD.ReidelPublishingCompany. INTERMOLECULAR FORCES: WHAT CAN BE LEARNED FROM AB INITIO CALCULATIONS? Advan der Avoird Institute of Theoretical Chemistry, University of Nijmegen, Toernooiveld, Nijmegen, The Netherlands. 1. INTRODUCTION Various experiments, suc~ as elastic or rotationally inelastic molecular beamscattering(1,2 and spectroscopic studies of so-cafled Van der Waals molecules(3,4), have been designed especially to provide information about the Van der Waals interactions between molecules.