Acoustical Imaging Keynote Papers Mathematics and Physics of Acoustical Imaging Transducers and Arrays Nondestructive Evaluation Geophysical and Underwater Ultrasonics Microscopy and Microscanning Scattering by Blood and Tissue Medical and Biological Image Formation Tissue Characterisation Tissue Motion and Blood Flow Elasticity Imaging Hard Tissues Novel and Emerging Methods. The origin ofthe International Acoustical Imaging Symposium series can be traced to 1967 when a meeting on acoustical holography was held in C alifornia. In those days acoustical holography was at the leading edge of research but as the importance of this subject waned so the title of the series was changed from Acoustical Holography to Acoustical Imaging in 1978. The early Symposia were held at various venues in the United States. In 1980. the series became international with the Symposium that year taking place in Cannes in France. The pattern now is to try to met alternately in the USA and in another part of the world so that active researchers everywhere can conveniently attend at a reasonably high frequency. It was a great privilege for us in Bristol in the United Kingdom to be chosen to host the 25th Symposium which convened on 19 March 2000 and spread over four days. We were blessed not only by good weather but also by the attendance ofnearly 100 pa rticipants who came from 17 c ountries. A large number of papers were accepted for presentation either orally or as posters. Whether an oral presentation or a poster all were considered to have equal merit and no distinction is made between them in the published proceedings. There were no parallel sessions so every participant could attend every presentation. The re sultant disciplinary cross fertilisation maintained the t radition of past Symposia.