PREFACE The Second* Conference on Radioactive Fallout from Nuclear Weapons Tests, sponsored by the U. 8S. Atomic Energy Commission, was convened at the AEC headquarters, Germantown, Md., Nov. 3 to 6, 1964, under the auspices of the Division of Biology and Medicine. Papers were invited from among groups conducting research in the field supported at least in part under the research programf of the Fallout Studies Branch, Division of Biology and Medicine. There were two exceptions: Dr. Joseph B. Knox was asked to present studies of current interest related to local fallout from peaceful nuclear explosives (Operation Plowshare) detonations, and Dr. Howard A. Hawthorne was asked to present results from his studies, which have close relations to projects under the Fallout Studies Branch program. Many persons in the United States outside the program were invited to attend the conference and to participate in the discussions. Much progress in understanding fallout mechanisms has been made by investigators throughout the world since the last such conference in 1961. Much new information that is useful in forming a sound basis for fallout prediction was presented. It can be concluded that a great deal of work has been and is being done toward elucidating fallout mechanisms from the source of nuclear debris to its contact with man. This is reflected by the greater sophistication of the studies and by *The proceedings of the first conference, held at Germantown, Md., Nov. 15 to 17, 1961, have been published. [A. W. Klement, Jr. (Ed.), Radioactive Fallout from Nuclear Weapons Tests, USAEC Report TID-7632. (Bks. 1 and 2), February 1962.] Available from the Clearinghouse for Federal Scientific and Technical Information, Na- tional Bureau of Standards, U. 8S. Department of Commerce, Springfield, Va., 541 pp. (2 books), $5.75. tThe entire program, Atmospheric Radioactivity and Fallout Re- search, is described in USAEC Report TID-12616(Rev. 1), December 1962. Available from the Clearinghouse for Federal Scientific and Technical Information, National Bureau of Standards, U. S,. Depart- ment of Commerce, Springfield, Va., 95 pp., $1.00. iv