Volume 15 follows the format of earlier volumes in the series. The contents give the next installment in the varied aspects of acoustical imaging research. On this occasion, some emphasis was placed on the rela tionship of l1nderwater acoustics to acoustical imaging and a volume of papers under the title Underwater Acoustics Proceedings from the 12th ICA Symposium held in Halifax, will appear at roughly the same time as this volume. There is no duplication in these volumes but they are in terlinked, at least to the extent that papers from common conference sessions appear in one or another volume. An innovation is the review paper presented at the beginning of the volume A History of Acoustical Imaging, by G Wade. This fairly detailed review comes at a point in time when so much has been achieved and in some cases passed by, that a record of some of the earlier work might help to keep a balance with the large collections of research papers which have appeared in the many volumes.