Membrane interaction is a large research area involving various disciplines. A symposium entitled "Cell and Model Membrane Interactions" which took place in Boston, MA during the 155th American Chemical Society Meeting, April 25, 1990, focused on membrane adhesion and fusion. The topics were explored in studies involving lipids, virus envelopes and cell membranes. Especially discussed, were the roles of polymers, lipids, and proteins on these membrane interactions. Fusion of membrane is an important molecular event which plays a pivotal role in many dynamic cellular processes, such as exocytosis, endocytosis, membrane genesis, viral infection processes, etc. The process includes adhesion of the mem­ branes, fusion, and finally reorganization of the components of the two membranes. The basic notion shared during the symposium was that membrane hydro­ phobicity, especially local membrane hydrophobicity is one of the important factors contributing to membrane fusion. Most of the papers are collected here and they are arranged approximately in the same order as they were presented at the sympo­ sium. These papers are the most up-to-date and representative work at the forefront in each membrane interaction field. I sincerely hope the reader will gain further understanding on membrane interactions especially, membrane and vesicle fusion phenomena through this symposium proceedings volume.