This book contains 17 invited papers and 80 communicated papers presented at the International Symposium on Physical Acoustics, held at the University Campus of Kortrijk, Belgium, from 19-22 June 1990. The twenty-fifth anniversary of the Campus was celebrated with special activi ties such as concerts, exhibitions and scientific meetings. This symposium was a part of the celebration. The 120 participants came from 18 different countries. Among the largest groups we mention 32 French contributions and 19 contributions from the U.S.S.R. We especially thank Prof. V.V. Proklov from Moscow and...