explains all these aspects, and also discusses how the evolution of stars determine that of galaxies. The most interesting observations are illustrated by spectacular images, while the theory is explained as simply as possible, without however avoiding some mathematical or physical developments when they are necessary for a good understanding of what happens in stars. Without being a textbook for specialists, this book can be profitably read by students or amateurs possessing some basic scientific knowledge, who would like to be initiated in-depth to the fascinating world of stars. The author, an emeritus astronomer of the Paris Observatory, worked in various domains of astronomy connected with the subject of this book: interstellar matter and evolution of stars and galaxies. He directed the Marseilles observatory from 1983 to 1988 and served for fifteen years as Chief Editor of the professional European journal Astronomy & Astrophysics. He has written many articles and books about physics and astronomy at different levels.