Ground-based observations have detected solar-like oscillations on Sun-like stars, and diagnostics similar to those used in helioseismology are now being used to test and constrain the physics and evolutionary state of these stars. Multi-mode oscillations are being observed in an abundance of other stars, including slowly pulsating B stars (SPB stars), delta-Scuti stars, Ap stars and the pulsating white dwarfs. New classes of pulsators continue to be discovered across the Herzsprung-Russell diagram. Yet the challenges still to be faced to make asteroseismology across the HR diagram a reality are formidable. Observation, data analysis and theory all pose hard problems to be overcome. This book aims to facilitate a cross-fertilisation of ideas and approaches between fields covering different pulsators and with different areas of expertise. It covers most known types of pulsators, reflecting a productive and far-reaching interchange of ideas, which should make it a useful reference for researchers and postgraduate students working on stellar structure and evolution.