The solar corona is not easily observable from the ground; only with the coronagraphs located in high mountains or at infrequent and short occasions of total eclipses. And in any case these observations are limited to the corona beyond the solar limb. Therefore, it is natural that our understanding of the physics of the solar corona has advanced dramatically by sustained observations from space-based platforms, like Skylab in the 1970’s. These several years are particularly notable in this respect, because of a wide variety of data from Yohkoh, Ulysses, and SOHO.