This publication presents the culmination of collaborative effort between specialists in the wide range of disciplines concerned with the effects of ionizing radiations on nucleic acids. The authors belong to a group formed under the aegis of the Com mission of the European Communities some eight years ago with the object of facilitating the exchange of ideas and inforrration between European scientists working in this field. The Commission'S aim was not to replace traditional information channels, but to strengthen the various links between the scien tists in the group, as if they were working together in a single team. In addition to the annual meetings of the group, contact was maintained by individual visits, exchanges of young scientists, experiments using mutual equipment, and the regular publication of a Newsletter, mainly to announce the availability of preprints. Bruxelles, December 1977 A. J. Bertinchamps Commission of the European Communities. Preface Mankind today is faced with a choice of cardinal importance, namely, deciding on the source and quantity of energy to be made available for tomorrow's world. If, as is probable, the energy is to be mainly of nuclear origin, we must expect a marked ex pansion of the nuclear industry, which could well become the world's leading industry in the not-too-distant future. This would carry with it the problems caused by the presence of enor mous quantities of radioactivity, despite the stringent precau tions taken to date and those to be taken in future.