The magnetic fields of the Earth, the planets and the sun, provide a basis for the basic structure of our solar system. The geomagnetic field has been explored and measured for centuries, and it is known that it experiences major changes on time scales ranging from seconds to millions of years. These changes are associated with the internal source of the geomagnetic field, which is not completely understood. Measurements conducted by spacecraft during the last few decades, have explored the geomagnetic field and revealed details about both internal and external sources. The external sources are associated with the complex system of currents that flows in the “comet-like” configuration of the distant geomagnetic field called the magnetosphere, which is produced by the solar wind. The magnetic fields due to the external sources can vary with time scales from a few seconds to several years, related to solar cycle activity. The study of these phenomena span scientific disciplines extending from the geophysics of the Earth's core to solar and space plasma physics. A crucial element of this study is the continuous and accurate monitoring of the geomagnetic field and the appropriate means to archive this important data set.