This proposed workshop on Sources, Transport, Energization and Loss of Magnetospheric Plasmas will focus on all aspects of the modeling of magnetospheric plasmas, and specifically will tie in to the international Solar Terrestrial Energy Program (STEP), the upcoming ISTP and IMI spacecraft missions, and the NSF Geospace Environment Modeling (GEM) program. Workshop sessions will involve seven oral sessions including four tutorial talks per session with extended discussion time. These sessions will cover the topics of Distribution, Sources, Transport, Energization, Loss, Imaging, and Synthesis (summary of existing consensus and outstanding issues). Contributed papers will be in two evening poster sessions. The workshop will be held at Guntersville Lodge south of Huntsville, Alabama.