The Solar, Anomalous, and Magnetospheric Particle Explorer, or SAMPEX, was the first of NASA’s Small Explorer missions. SAMPEX was designed to study the characteristics of four types of charged particles that come from outside Earth’s magnetic environment: galactic cosmic rays, which are created by supernovas in the Milky Way; anomalous cosmic rays, which come from the interstellar medium surrounding the solar system; solar energetic particles, which come from the sun; and magnetospheric electrons, which are particles from the solar wind that become trapped in Earth’s magnetic system. SAMPEX observations provided important new information about the cosmic abundances of elements, the composition of the nearby interstellar medium, the structure and processes that drive the sun, and the process by which the solar wind injects energy into Earth’s upper atmosphere.