Advances in Radiation Biology, Volume 2, reflects a continuing effort to provide wide-ranging analyses of progress in various phases of radiation research. The articles cover a spectrum of topics varying from the initial physical events which allow us to discriminate color, to the chemical and biological processes which determine the extent and permanence of radiation damage, and finally to the role of genetic control and damage in determining the fate of irradiated cells. The basic emphasis of the articles also varies. In some, the main attempt is to review extensively the available data so as to evaluate the possible contributions of various mechanisms to a given phenomenon. One article is devoted an evaluation of one physical approach which appears to be a promising way of understanding color perception. These different treatments should be of value not only to the researcher but also to the student, inasmuch as each approach is invariably dictated by the state of the art in the area being covered.