At many stages of their lives, stars exhibit variability due to pulsations or oscillations. These oscillations give us a window to ‘inside the star’, to infer its interior structure and composition, and to test the physics of stellar models. The calibration of stellar luminosity with pulsation period allows us to measure distances within the Milky Way and to nearby galaxies. This volume describes the latest observational and theoretical research and remaining challenges for understanding pulsating variable stars of all types.