What have psychologists (and others) discovered about the process of scientific discovery?

We describe four major approaches to the study of science-historical accoun ts of scientific discoveries, psychological experiments with nonscientists working on tasks related to scientific discoveries, direct observation of o ngoing scientific laboratories, and; computational modeling of scientific d iscovery processes-by viewing them through the lens of the theory of human problem solving. We compare and contrast the different approaches, indicate their complementarities, and provide examples from each approach that conv erge on a set of principles of scientific discovery.