Advances in Solar Energy, now in its fifth year, is continuing with topics of the main field of solar energy conversion. However, because of the increasing interest in a solar systems approach, we have decided to include the article of Bockris et al., on Hydrogen Technology, which offers interesting aspects of transport and storage of solar energy, as well as the potential for a versatile fuel. The other articles cover the field of photovoltaics, solar energy-related mate­ rials, wind conversion, solar retrofitting of existing buildings, and new architectural designs in harmony with climate and the comfort of all occupants. These articles give a critical assessment of the present state of the art, and provide a long list of literature for further in-depth studies. I greatly appreciate the assistance of the Editors and referees of the articles for their many constructive suggestions. My special thanks go to Ms. Martha Hobbs for her dedicated work in typesetting the manuscript in the University of Delaware's Publication Office, and to the University of Delaware for their continued support. The accommodating help from Plenum Press and its production staff deserves our grateful acknowledgement.