Based on lectures given at a CNRS summer school in France, this book covers many aspects of stellar environments (both observational and theoretical) and offers a broad overview of the field. More specifically, Part I of the book focuses on the Sun, the properties of the ejected plasma, of the solar wind and on space weather. The second part deals with tides in planetary systems and in binary stellar systems, as well as with interactions in massive binary stars as seen by interferometry. Finally the chapters of Part III discuss the very close environments of young stars; Stellar Winds, Magnetic Fields and Disks; Magnetic field and convection in the cool supergiant Betelgeuse; The formation of circumstellar disks around evolved stars; and an introduction to accretion disks is given. With its broad approach the book will provide graduate students with a good overview of the environments of the Sun and stars.