This paper shows an overview over a doctoral thesis project which focuses on Collaborative Information Seeking (CIS) with a core interest in searcher heterogeneity. A special field of interest is the way how different personalities interact in a collaborative search scenario and if heterogeneous groups perform better or worse than homogenous groups. The goal is to provide a description of group performance in CIS, to get suggestions for the design of collaborative search tools and to create a model of CIS integrating search heterogeneity.