Physical Acoustics: Principles and Methods, Volume VIII discusses a number of themes on physical acoustics that are divided into seven chapters. Chapter 1 describes the principles and applications of a tool for investigating phonons in dielectric crystals, the spin phonon spectrometer. The next chapter discusses the use of ultrasound in investigating Landau quantum oscillations in the presence of a magnetic field and their relation to the strain dependence of the Fermi surface of metals. The third chapter focuses on the ultrasonic measurements that are made by pulsing methods with velocities obtained through phase comparison methods and attenuations obtained through comparing pulse heights for successive reflections. In Chapter 4, methods for measuring the properties of solids and liquids at very high pressures are described. Chapter 5 explores some of the relationships between the thermal equilibrium properties of solids and mechanical properties such as the second- and third-order elastic constants. The sixth chapter discusses the interaction of sound waves with thermal phonons in dielectric crystals and emphasizes the relationship between the various theories proposed and the effect of phonon interactions on the velocity of sound. The last chapter describes the applications to metals and rock mechanics of internal friction at low frequencies due to dislocations. This book is beneficial to students and physicists conducting work on physical acoustics.