Physical Acoustics: Principles and Methods, Volume XII, covers the fundamental physical phenomena and important engineering applications of physical acoustics. This volume is composed of five chapters, and begins with the presentation of the theoretical concepts and experimental data concerning the role of long-wavelength acoustic phonons in Jahn-Teller phase transitions. The second chapter highlights the use of superconducting tunneling junctions as phonon generators and detectors followed by a discussion on ultrasonic wave propagation in glasses at low temperatures in the third chapter. The fourth chapter explores various integral transform methods for describing the elastic response to acoustic pulsed. These methods include spatial Fourier and/or Bessel transforms the Watson-Sommerfeld transformation or the Poisson summation formula, and the Fourier or Laplace transform for the time behavior. The final chapter outlines the measurement methods for ultrasonic phase and group velocities and attenuation together with their industrial applications.