This dissertation is a result of an industrial PhD fellowship education (EF-881) madein cooperation between FORCE Technology, Aalborg University and The Industrial PhD Fellowship Programme Board at The Danish Academy of Technical Sciences, ATV. The education is financed by funding from The Ministry of Science,Technology and Innovation. The work started in October 2000, and I have since then worked part time on the project and part time as psychologist in FORCE Technology, Division of Maritime Industry, Department of Training, Ports and Human Factors. The dissertation is handed in as a PhD dissertation at University of Aarhus but has at the time of publication not yet been accepted for assessment. The dissertation is written as a collection of papers with an introduction to frame the papers. The papers are written in the period from 2001 to 2006. The work is based on many onboard studies, simulator studies, observations, interviews and measurements of EEG (brain wave activity) in laboratory (the simulator) and on board different types of vessels. It is also based on the knowledge and experience I have gained from participation (1) in several European Union projects about maritime safety, (2) in a number of differentdesign projects with the aim of designing improved user interfaces e.g. in maritimeequipment, (3) in studies of accident reports, (4) in teaching of seafarers, health carepersonnel and control room operators etc. and (5) in training of accident investigatorsfrom the maritime domain, navy, insurance companies and railways. I have worked with human factors in many domains including the maritime domain,off-shore industry, power plants and hospitals, and the broad experience from these domains have helped me in the writing of the dissertation and the understanding of the applicability of the concepts, models, theories and classification systems mentioned.