This article explores the relationship between the concept of uncertainty in information seeking, within a model of the problem-solving process proposed by Wilson (1999a) and variables derived from other models and from the work of Ellis and Kuhlthau. The research has involved longitudinal data collection in the United States and United Kingdom employing three interview schedules (incorporating self-completed questionnaires) used for pre- and postsearch interviews: and postsearch interviews with the information seeker and the search intermediary. In addition, the Sheffield team employed a fourth set of instruments in a follow-up interview some 2 months after the search. Related search episodes, with a professional search intermediary using the Dialog Information Service and other sources were audiotaped, and search transaction logs were recorded. The mediated search clients were faculty and research students engaged in either personal or externally supported research projects. The article concludes that the problem solving model is recognized by such researchers as describing their activities and that the uncertainty concept, operationalized as here, serves as a useful variable in understanding information-seeking behavior. It also concludes that Ellis's concept of search characteristics and Kuhlthau's information-seeking stages are independent of the problem stage, and that a set of affective variables, based on those of Kuhlthau, appear to signify a generalized positive or negative affective orientation towards the course of the information problem solution.