Thematic survey of Jens Rasmussen's papers (and Risø work reports) from 1961 to 1986. Theme 1: Rasmussen's engineering epistemology. Theme 2: Rasmussen's approach of conceptualizing the problem of technical reliability as a systems problem. Theme 3: Rasmussen's conceptualization of the operator in technical contexts. Theme 4: Supporting the operator's everyday knowing and acting for correct functioning of the system. Theme 5: Emphasis on a generalized qualitative and categorical approach for systems design. Theme 6: Relation between operator and designer in systems design.