The purpose of this paper is to study the interactions between formal structures and knowing communities and to show how formal structures can support external communities. Indeed, the literature reveals the critical role of external knowing communities for innovation. This research is based on a sequential mixed-method research design with a multi study sequential approach. Three studies are performed to analyze the interactions between IT formal structures and open source communities. Study 1 and study 3 are quantitative and rely on the same sample of 157 IT business managers. Study 2 is qualitative and is based on four managers of three formal structures deeply rooted in open source communities. These studies show that the use of open source within the formal structure has an impact on the three forms in which formal structures involve themselves in external knowing communities: formalized, result-oriented and inter-connected involvement. They also reveal the diffi­culties and possibilities of inter-connected involvement and highlight the central role of formalization in com­munity involvement.