Various studies focus on general networks within and between organizations, but strongly focused studies on knowledge sharing through social networks and communities within specific domains that are of critical relevance to the R&D organization are hard to find. Therefore, the argument presented here is explored through an empirical case study on inter-organizational knowledge community building between different research institutes of the Fraunhofer-Gesellschaft, a large German organization for contract research in all fields of the applied engineering sciences. Expert knowledge communication and networking processes are evaluated by a multi-level approach. Institutionalization of knowledge transfer is studied with regard to the development of the informal contacts between the community members and the inter-organizational linkages on an aggregated level. The main focus is put on the relationships of knowledge exchange between the formal organizational boundaries and the informal interorganizational network structures. Finally, this case study aims at further supporting the adaptation of methods from social network analysis for purposes of organization and management practice.