This book begins with a very readable survey "The Sun Today" by J.-C. Pecker. It is followed by thorough reviews from leading experts covering theory and observations. The focus shifts from the solar core, studied via neutrino emissions and helioseismology, through the interface regions where it is believed the large-scale magnetic fields are generated, to the corona, where most of the high temperature phenomena characteristic of this region may be studied directly. As energetic particles play such a vigorous role in this part of the sun, a separate session was devoted to their transport and storage in the corona.