With the International Solar Terrestrial Physics (ISTP) constellation of spacecraft, plus key measurements from other scientific and operational spacecraft, it is possible to study the flow of energy from the sun through the interplanetary medium into the magnetosphere and upper atmosphere of the Earth. We use Yohkoh soft x-ray images to identify large solar coronal holes. These solar regions give rise to high-speed solar wind streams which are detected and characterized by measurements from the WIND spacecraft. The high speed streams drive the Earth’s magnetosphere quite substantially giving rise to strong relativistic electron acceleration throughout the outer radiation zone. The SAMPEX spacecraft in low Earth orbit and the MCP package onboard a high-inclination, elliptical-orbit satellite map the electron belts as they wax and wane under solar wind stream influence. New measurements from the CEPPAD investigation of the POLAR spacecraft are able to examine the spectral and angular distribution properties of accelerated magnetospheric electrons with unprecedented resolution. These data show that the Earth’s magnetosphere is a strong accelerator of high energy electrons. Thus, the ISTP program may be able to contribute substantially to an important aspect of plasma astrophysics.