This volume contains the proceedings of the Fourth International Conference on Phonon Scattering in Condensed Matter held from August 22-26, 1983 at the University of Stuttgart. The preceding conferences were organized at Saint Maxime and Paris in 1972, at the University of Nottingham in 1975, and at the Brown University Providence/Rhode Island in 1979. The Stuttgart conference, like the preceding conferences, was mainly concerned with "propagating" high-frequency acoustic phonons, mechanical waves and heat up to the lattice limiting frequency. Lattice dynamics, optical pho­ nons, phase transitions, etc., were included as far as they are involved in acoustical phonon scattering, propagation and generation. In this context the conference covered all aspects of acoustical phonon physics, especially generation of phonons, propagation, scattering and detection. Since acoustic phonons participate in most energy-transfer processes in solids and liquids, the field of interest is growing rapidly. Therefore exciting new developments of acoustic phonon physics could be presented at the Stuttgart conference as well as important progress with respect to well-known problems, as, for example, the Kapitza resistance. Two hundred and six scientists from 21 countries attended the conference. Thirteen invited papers and 105 contributed papers, with 34 as posters, were presented. The discussions are included in this volume. A discussion session on large wave vector phonons was organized and chaired by V. Narayanamurti. A discussion session on phonon scattering at interfaces was organized and chaired by R.O. Pohl.