About the authors JENS RASMUSSEN was a research professor of cognitive systems engineering at Ris? National Laboratory and the Technical University of Copenhagen, following 25 years as the head of the Electronics Department at Ris? National Laboratory (then Atomic Energy Research Establishment Ris?). Since 1962, he has conducted research in the areas of reliability and risk factors, human reliability, work domain taxonomy, human-machine interaction, and ecological information systems design. A distinguished leader in the aforementioned fields, he has chaired a number of groups of international experts appointed to assess risk and human-machine interaction in nuclear and other hazardous industries. He is now a consultant in cognitive systems engineering and risk management. ANNELISE MARK PEJTERSEN is a Senior Scientist with the Cognitive Systems Group at Ris? National Laboratory. She was an acting professor at the Royal School of Librarianship and manager of the Danish Labor Union's Center for Informatics. Her main areas of expertise developed from the early 1970s and include the taxonomy of work domains, cognitive engineering methods for system design and evaluation, cognitive work analysis, multimedia interfaces, ecological interface design, information indexing and retrieval, and the analysis and modeling of user behavior. She holds several prizes for her results in the design and evaluation of information retrieval systems based on field studies. L. P. GOODSTEIN was a senior scientist of the Electronics Department of Ris? National Laboratory for 25 years. He started work in the human-machine area in the early 1960s by designing and operationally evaluating a control console including dynamic graphic displays for a nuclear reactor. His fields of expertise include the analysis, design, and evaluation of decision support systems, human-computer interfaces, information displays for process control, and the design and use of process simulators for human-machine system research. He is now a consultant in human-machine systems design and evaluation.