The plasmasphere is the vast doughnut-shaped region of the magnetosphere that forms a cold thermal plasma cloud encircling the Earth, terminating abruptly at a radial distance of 30,000 km over a sharp discontinuity known as the plasmapause. This is the first monograph to describe the historical development of ideas concerning the plasmasphere by the pioneering researchers themselves. The monograph brings our picture of the plasmasphere up to date...