SUMMARYThis paper applies the expertise approach to cooperation settings and examines high performers' knowledge about cooperation situations. We argue that high performers know more about how to address cooperation situations than do moderate performers. Specifically, we assume that they know more about problem analysis, about how to address the task, the cooperation partner and the cooperation partners' task approach. We report findings of two empirical studies in which study participants responded to scenario situations. The first study based on a sample of 39 software professionals showed that high performers were superior with respect to overall knowledge and specific knowledge aspects. The second study based on a sample of 62 engineers partially replicated these findings. High performers' better knowledge of cooperation situations could not be explained by years of experience or perspective taking. However, situation specific experiences partially accounted for the relationship between performance level and knowledge.The question of what distinguishes high from moderate performers is one of the core questions of research on expertise (Ericsson and Lehmann, 1996;Ericsson and Smith, 1991a). Empirical studies within this research area showed that high performers possess exceptional domain-specific knowledge and superior problem-solving skills (Groot, 1978;Koubek and Salvendy, 1991;Vessey, 1986). Most of this research is based on the study of individuals meeting domain-specific, mainly cognitive task requirements in individual task settings. However, in modern organizations, the work situation of many professionals is characterized not only by high cognitive but also by high cooperation requirements (Clegg et al., 1996;Keenan and Newton, 1987). In professional areas such as software design, product development, or engineering, many tasks are not any longer accomplished in individual task settings, but in team-based working environments. Thus, for an individual it is not enough to possess domain-specific knowledge and problem-solving