Originally published in 1957, this book contains twenty-three contributions from a symposium held during the Ninth General Assembly of the International Astronomical Union in Dublin. The papers contained range from present knowledge in stellar instability to the presentation of new research results and focus on the instability among the hot stars of both low and high luminosity and the cool stars and their close binary systems. Papers range from 'Physical processes in novae' to 'Variable stars and problems of stellar formation' to 'Photometric evidence of instability in eclipsing systems'. Accounts of discussion, which followed the presentations, are also included for reference as well as photographs and diagrams. Offering a re-assessment of non-stable stars and recognising, relocating and redefining the issues surrounding stellar instability, this book will be a valuable reference work to anyone interested in the history of physics, astronomy and cosmology.