The Expert Committee on Biomaterials and Biotechnology for the European and the North American Region was founded by the General Assembly of UNESCO at its 21st Session, in 1981. The Committee comprises a Coordinating Group and four working Groups, defined in the following scientific areas: Group I Proteins: source, structure and function. Group II Nucl~ic acids: the hereditary materials. Group III Im~une materials and mechanisms. Membranes and transport in biosystems. Group IV In fulfilment of one of the objectives of the Committee, which have been adopted by the General Assembly of UNESCO in 1981, namely the intensification of the exchange of scientific information on biomaterials and biotechnology, working Group IV organized an international workshop on Ion Interactions in Energy Transport Systems, which was convened in Athens, Greece, from 8 to 12 April, 1985. Scientific papers presented at that workshop make up the chapters presented in this volume. The present volume focusses on natural and artificial membranes that are involved in energy transduction. Several chapters are devoted to membranes and membrane components that convert and utilize light, such as the thylakoid membrane of oxygenic photosynthetic organisms (eukaryotic and prokaryotic), the chromatophore membrane of nonoxygenic photosynthetic bacteria and the purple membrane of the halophilic bacteria. Other systems examined include the mitochondrial membranes and their adenine nucleotide carrier, the plasma membrane of animal cells, and lipid bilayer vesicles, either reconstituted or not, with enzymes.