This book contains the lectures presented at the Summer Advanced Study School, 'Magnetospheric Particles and Fields' which was held at Graz, Austria during the period August 4-15, 1975. One hundred and one persons from fifteen different countries attended the Schoo!. The authors and publisher have made a special effort for rapid publication of an up-to- date status of particles, fields, and processes in planetary magnetospheres. Special thanks are due to the lecturers for their diligent preparation and excellent presentations. The in- dividuallectures and the published papers were deliberately limited; the authors' cooper- ation in conforming to these specifications is greatly appreciated. Many thanks are due to Drs C. D. Anger, Gerhard Haerendel, George P. Haskell, Carl McIlwain, Vytenis Vasy- liunas, Martin Walt, and James Warwick who served as session chairmen during the School and contributed greatly to its success by skillfully directing the discussion period in a stimulating manner after each lecture. Many persons contributed to the success of the School. Drs C. D. Anger, Carl-Gunne Falthammar, Gerhard Haerendel, George P. Haskell, Carl McIlwain, David Nunn, Willi Riedler, Finn S[raas, Vytenis M. Vasyliunas, Martin Walt, and James Warwick were especially helpful in preparing the technical program. Dr Willi Riedler assisted in ar- ranging for the facilities in Graz. Drs Gerhard Kremser and Martin Friedrich were most helpful with many aspects of the local arrangements in Graz. The assistant editor, Mrs Diana R. McCormac, checked the manuscripts and proofs, and worked hard to achieve a uniform style in this book.