The Third International Conference on Phonon Scattering in Condensed Matter was held at Brown University, Providence, Rhode Island from August 28-31, 1979. The previous conferences in this series were held at Nottingham in 1975, and in France at Paris and Ste Maxime in 1972. Until about 15 years ago phonon scattering was studied almost exclusively by measurements of thermal conductivity. This approach has the severe limitation that the result obtained for the phonon scattering rate is actually the average of the scattering for all of the phonons in the sample. Thus, no distinction can be made between phonons of different polarization, direction of propagation, or energy. During the 1960's several significant developments occurred. The most important of these was the application by Von Gutfeld and Nethercot of the "heat-pulse" method, previously used only in liquid helium, to the investigation of phonons in crystals. This approach makes possible the study of the propagation and scat­ tering of phonons of known polarization and propagation direction. The early heat-pulse experiments used phonon generators which pro­ duced phonons having a broad distribution of energies and, in addi­ tion, the phonon detectors were sensitive to phonons of all energies.