Knowledge integration is a critical topic in current knowledge management research and practice. Research on this topic focuses primarily on how knowledge is integrated within a work setting. A less researched area is knowledge integration between different work groups, which is the focus of this paper. The paper presents two intensive case studies—one permanent work setting and one temporary (project) work setting—which were studied using a practice-based perspective. The purpose is to describe and explain how knowledge is integrated between different work groups and we address why is it that boundary activities work or break in knowledge integration. A main result of the study is that knowledge integration in the two cases was more complicated than the literature suggests. Differences in knowledge and organizational landscapes made knowledge integration a challenging task. Both differences and similarities were found between the two cases. Differences were seen in the use of boundary spanning activities and boundary objects. Similarities that were found were, for example, organizational structures and mechanisms, i.e. purposes, rules, and infrastructures, which facilitated the integration of knowledge or could function as obstacles and impediments.