JUHAN FRANK is Professor of Physics and Astronomy at Louisiana State University, where he currently teaches astronomy and astrophysics, and carries out research on mass transferring binary stars and active galactic nuclei. He obtained his PhD in astrophysics from Cambridge University, and has held positions at the Astronomy Centre in Sussex, the University of Leicester, and the Max-Planck Institute, Munich. ANDREW KING is Professor of Astrophysics at the University of Leicester, and resident Director of the UK Astrophysical Fluids Facility. His research centres on accretion and the evolution of the host systems. He has held a Senior Fellowship of the UK Particle Physics and Astronomy Research Council, and visiting appointments at many centres of astrophysical research in Europe, the USA and Australia, including visiting professorships at the Universities of Paris and Goettingen. DEREK RAINE is Senior Lecturer in Theoretical Astrophysics at the University of Leicester, where he works on active galaxies and cosmology. He is Head of Physics Teaching and has co-authored several text books. He obtained his PhD in general relativity from Cambridge University.