The text of this volume had its origin in the Tenth Annual Conference on Applications of X-Ray Analysis sponsored by the University of Denver and held August 7,8,9, 1961, at the Albany Hotel in Denver, Colorado. Approximately 300 participants derived benefit from the presentation of fifty-six papers on new scientific and technological developments in X-ray methods and the discussions that followed. Forty-eight of these papers plus one presented at the Ninth Con ference and cleared for publication too late to be included in Volume 4 are given here. The growth of the annual conferences and the breadth and intensity of the presentations are confirmations of the observation that the field of X-ray re search is indeed in a state of rapid and healthy development. Financial assistance provided by the United States Office of Naval Research permitted the participation oftwo distinguished scientists from Europe, Professor Andre Guinier of the University of Paris and Professor Hans Nowotny of the University of Vienna.