The idea of a magnetic field in space around Earth began 400 years ago with Gilbert's recognition that the magnetic field of Earth extends outward into space to form what we now call the magnetosphere. The concept of the solar wind and the heliosphere had its first glimmerings with the recognition, about 270 years ago, that geomagnetic activity is correlated with solar activity. It was suggested about a 100 years ago that the connection is through solar corpuscular radiation with velocities of the order of 103 km/s. The observed acceleration of comet tails indicated the universal nature of solar corpuscular radiation, giving rise to the first speculation on the existence of the heliosphere. The hydrodynamic expansion of the million degree solar corona was then shown to provide the solar wind (solar corpuscular radiation), stretching out the magnetic fields of the Sun to fill the heliosphere with a spiral magnetic field. The advent of the space age soon verified the solar wind and magnetic field with direct measurements. ¿ 2001 American Geophysical Union