the fact that, as more is learned about fallout, more specific and detailed studies are possible; improvements in equipment also have contributed. Several papers showed that studies conducted during atmospheric tests in 1961 and 1962 contributed greatly to our knowledge of fallout mechanisms. Of particular importance is the Springfield Program, a coopera- tive program with the Department of Defense, which permitted detailed studies of rainout as well as studies of mass transfer between the stratosphere and the troposphere. It has been clear for some time that the various mechanisms hypothesized cannot be described adequately by simple models. However, recent studies have provided information on certain fallout problems which permits better fallout predictions and assessments than was possible several years ago. For prediction methods of greater accuracy, applicable to all types of currently anticipated sources of atmospheric nuclear debris, further studies are necessary, including more information about the characteristics of the sources of fallout material. Other areas needing further detailed study were discussed. Discussions are included in these proceedings. In some cases, the record was not adequate to permit transcription. For both the published papers and the discussions, authors and speakers had an opportunity to edit the manuscripts and transcripts. Since time for oral presentations of papers was limited, the published papers are considerably more detailed than the conference presentations. An attempt has been made to formalize the style of the proceedings, which, in general, follows that of previous books in the AEC Symposium Series. Acknowledgment is due the Division of Technical Information Extension, Oak Ridge, Tennessee, for publishing assistance, particularly to Margaret L. Givens and Charles W. Carroll for their editorial help and to William E. Bost for his preparation of the index. We wish to acknowledge with thanks assistance from many persons who helped in planning and conducting the conference. First are the session chairmen, who, although not responsible for the agenda, introduced the papers and conducted the discussions. Many administrative details were planned and executed by Robert C. Brothers, Chief, and other members of the Administrative Branch, Division of Biology and Medicine. R. W. Beadle, E. W. Bierly, W. F. Marlow, and J. E. Miller of the Fallout Studies Branch provided much as- sistance in preparing for and conducting the conference. Clara Mae Baker, Lydia Barchers, Georgetta Blasingame,