Patrick Norman is Professor and Head of Theoretical Chemistry and Biology at KTH Royal Institute of Technology, Stockholm, Sweden. His research interests include response theory for non-resonant and resonant external fields in the UV/vis and X-ray regions. He is a co-author of the Dalton program. Kenneth Ruud is Professor of Theoretical Chemistry at the University of Tromsø The Arctic University of Norway. His research interests include linear and nonlinear response theory for mixed electric and magnetic fields as well as vibrational and medium effects. He is a co-author of the Dalton program. Trond Saue is a directeur de recherché of the French National Center for Scientific Research (CNRS) working at Université Toulouse III-Paul Sabatier in France. His research focuses on relativistic methods in theoretical chemistry. He is a principal author of the DIRAC program.