The book contains courses taught to a public of Ph. D. students, post-docs and con?rmed researchers in all ?elds of heliospheric plasma physics. It aims at identifying physical issues which are common to two di?erent ?elds of astr- omy: solar and magnetospheric physics. Emphasis is given to basic processes of transport and conversion of energy: magnetic reconnection is discussed in detail from the viewpoints of MHD and kinetic physics. Processes of charged particle acceleration are reviewed and confronted with recent observations. The subject is introduced by a summary of MHD and the basic structures and parameters of the solar atmosphere, terrestrial ionosphere and mag- tosphere are reviewed. The book combines a pedagogic and comprehensive presentation of physical issues and raises fully open questions, with the c- plementary and sometimes con?icting views of geophysicists and solar phy- cists. The book's focus, while basic, opens new avenues. Observatory of Meudon, France Ludwig Klein IAS, Orsay, France Jean-Claude Vial OCA, France Jean-Pierre Rozelot August 2000 The Editors Preface Following the great success of the ?rst two CNRS Summer Schools on Solar Astrophysics held in Oleron (May 1996 and May 1997 - two schools devoted to the highlights of solar physics), I came to the conclusion that the initiative should be continued."