This project addressed the question: What knowledge and processes enable individuals to construct and modify representations of novel, nonroutine problems? The theoretical goal was to extend the information-processing theory of problem solving to include processes that have been characterized as restructuring of problems and productive thinking by Gestalt psychologists such as Duncker (1935/1945) and Wertheimer (1954/1959). Three lines of research were carried out. One investigated different kinds of knowledge that result in problems that are routine, semiroutine, or nonroutine, according to distinctions in a simulation model that was developed in the project. Experiments distinguished between functional knowledge, involving relations between components of a device, and component knowledge, involving information about behavior of components independent of their interconnections. A second line of work studied processes of generating representations of physics problems, and identified important interactions between everyday experience-based knowledge about motions of objects and knowledge of theoretical principles. The third line of research studied processes of understanding and solution of back-of-the-envelope problems, and identified use of general methods for reasoning about quantities that are combined with domain-specific information. (Author/RH)