The International Sun-Earth Explorer (Isee) mission is a triple-spacecraft project that has been undertaken jointly by The National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA). The aim of this project is to make a comprehensive attack on the more obstinate problems of magnetospheric physics. The novelty of this mission is that two of the spacecraft, Isee 1 and Isee 2 (see Figures 1 and 2) circulate a known and controllable distance apart in the magnetosphere. They carry carefully matched payloads and can separate the ambiguities of time and spatial variations which beset measurements taken from a single platform. The apogee of the orbit (23 Re) was chosen so that the maximum number of bow shock and magnetopause crossings would be made during the mission. The third spacecraft, Isee 3 (see Figure 3), is stationed about 235 Re away from the earth on the earth-sun line. At this point it can observe features of the solar wind as they convect past on their way to produce perturbations at the magnetosphere. The mission is thoroughly integrated, and meaningful measurements rely heavily on simultaneous observations from all three platforms.