Our Sun is a variable star, with activity due to the presence of magnetic fields. These cause sunspots, flares, mass ejections, and a hot atmosphere called the corona. Such magnetic activity is common throughout all of astrophysics, but our Sun is one of the few objects which we can see with enough detail to provide strong tests of our theories. Unfortunately, the light emitted by the corona is primarily at wavelengths that are absorbed by our atmosphere and so do not reach the ground. We must therefore put our observing instruments into space and combine those observations with the data which can be obtained from the ground in order to study the full extent of solar activity.