The workshop on the "Molecular Basis of Polymer Networks", held October 5- 7, 1988 in 1iilich, FRG, continued a series of workshops jointly organized by the Institute Laue Langevin (ILL) in Grenoble, and the Institute of Solid State Physics of the KFA, 1iilich. The aim of this workshop was to provide a platform for discussions between theoreticians and experimentalists interested in the physics of polymer networks, in the hope that the two types of discussion would be synergistic. As revealed by the title of this workshop, the main focus of the lectures was on molecular aspects of the problem. The individual parts of these proceedings cover various approaches. Following quite general comments from a physicist examining the situation from "outside", various new theoretical concepts are developed. During the last decade the advent of Small Angle Neutron Scattering (SANS) has allowed the molecular structure of polymer networks to be studied and thus the reliability of the theories to be tested directly at the molecular level. Recent advances in this field are presented. The use of new techniques such as 2H NMR or QELS and the refinements of more classical, mechanical experimental measure­ ments have provided new information about the relation between the macroscopic behavior and the microscopic structure of polymer networks. Some recent results in this area are discussed for both chemically cross-linked networks and gels built by specific interchain interactions.