C. J. Joachain is Emeritus Professor of Theoretical Physics at the University of Brussels. His research activities concern quantum collision theory and the interaction of intense laser fields with matter. He has received many scientific awards and distinctions, in particular the Alexander von Humboldt Prize. He is a Fellow of the Institute of Physics and of the American Physical Society, and is a member of the Royal Academy of Belgium, of the Academia Europaea and of the European Academy of Sciences. N. J. Kylstra is currently employed in the financial services industry, and is a research fellow at the University of Brussels. His research interests include the interaction of atoms with high-intensity laser fields. R. M. Potvliege is currently Reader in Physics at the University of Durham. His research interests cover the theoretical aspects of multiphoton processes in intense laser fields.