Carolus J. Schrijver is an astrophysicist studying the causes and effects of magnetic activity of the Sun and of stars like the Sun, and the coupling of the Sun's magnetic field into the surrounding heliosphere. He obtained his doctorate in physics and astronomy at the University of Utrecht in the Netherlands in 1986, and has since worked for the University of Colorado, the U.S. National Solar Observatory, the European Space Agency, and the Royal Academy of Sciences of the Netherlands. Dr Schrijver is currently principal physicist at Lockheed Martin's Advanced Technology Center, where his work focuses primarily on the magnetic field in the solar atmosphere. He is an editor or editorial board member of several journals including Solar Physics, Astronomical Notices, and Living Reviews in Solar Physics, and has co-edited three other books. George L. Siscoe received his Ph.D. in physics from the Massachusetts Institute of Technology (MIT) in 1964. He has since held positions at the California Institute of Technology, MIT, and the University of California, Los Angeles, where he was Professor and Chair of the Department of Atmospheric Sciences. He is currently a Research Professor in the Astronomy Department at Boston University. Professor Siscoe has been a member and chair of numerous international committees and panels and is on the editorial board of the Journal of Atmospheric and Solar Terrestrial Physics. He is a Fellow of the American Geophysical Union and the second Van Allen Lecturer of the AGU, 1991. He has authored or co-authored over 300 publications that cover most areas of heliophysics.