Since the first papers by E. N. Leith and J. Upatnieks on the subject of holography appeared in 1961, there has been a virtual explosion of research activity in the field. More than SOO papers and articles on holo­ graphy have appeared in the last ten years. Many applications of holo­ graphy have been proposed, and some of these are beginning to enter the realm of usefulness. One of the applications that appears to hold great promise is acoustic imaging by means of holography. The first papers on this subject appeared in 1966. but already research activity in the field is burgeoning. Tbree symposia whoUy devoted to acoustical holography have been held and tbe papers published in book form. The purpose of this book is to bring together the results of research in acoustical holography, some of it as yet unpublished, under one cover so that workers in holography, nondestructive testing, medical imaging, underwater imaging, and seismic exploration can decide whether this new technique can be useful to them.