Theoretical issues. Task knowledge structures: Psychological basis and integration into system design (H. Johnson, P. Johnson). Formal modelling techniques in human-computer interaction (G. de Haan, G.C. van der Veer, J.C. van Vliet). Errors and theory in human-computer interaction (P.A. Booth). Knowledge retrieval and frequency maps (G.M. Brown). Event controllability in counterfactual thinking (V. Girotto, P. Legrenzi, A. Rizzo). Computer programming and program debugging. Training of Pascal novices' error handling ability (C.M. Allwood, C.-G. Björhag). Models of debugging (D.J. Gilmore). Analogical software reuse: Emprirical investigations of analogy-based reuse and software engineering practices (A. Sutcliffe, N. Maiden). Database interrogation. An experimental study of the interpretation of logical operators in database querying (P.J.M.D. Essens, C.A. McCann, M.A. Hartevelt). Analysing the deep structure of queries: Transfer effect on learning a query language (L. Linde, M. Bergström). Adapting systems to differences between individuals (F. Jennings, D. Benyon, D. Murray). Text editing. Interference among text-editing commands: Fan-effects and the role of system consistency (M. Heydemann, R. Hoffmann, R. Schmidt). On the microstructure of learning a wordprocessor (Y. Wærn). Graphics design. The constraint satisfaction approach to design: A psychological investigation (F. Darses). Author index. Subject index.