This volume of the Space Sciences Series of ISSI contains review papers that were presented at the first ISSI Workshop on Source and Loss Processes of Magnetospheric Plasma in October 1996. The review papers cover all parts of the inner and outer boundaries of the magnetosphere (high-latitude ionosphere, plasmapause, magnetopause, and distant magnetotail). The volume is the first one to summarize current knowledge about the transport of plasma in both directions across the transition regions between the magnetosphere and its low-altitude and high-altitude neighbouring regions. It is primarily of interest to researchers and graduate students in space physics and astrophysics but should be part of the library of all research groups involved in space matters.