PER HELANDER is a research scientist at the Culham Science Centre of the United Kingdom Atomic Energy Authority. After obtaining his doctorate from Chalmers University of Technology in Göteborg, Sweden, he held a post-doctoral position at Massachusetts Institute of Technology, where he remains a regular visitor. His scientific interests include most topics of theoretical plasma physics, in particular kinetic theory. DIETER SIGMAR received his doctorate from the Technical University of Vienna where he is now a.o. Professor of Theoretical Physics. He has had a long career in the US Fusion Program, and is now retired from his position as head of the Plasma Theory Group at the Plasma Science and Fusion Center at Massachusetts Institute of Technology. He is a fellow of the American Physical Society, and Corresponding Member of the Austrian Academy of Sciences.