ICT infrastructure and information systems have come to play a vital role in globalization. Walsham (2008) highlights three major aspects of this phenomenon: software outsourcing, virtual teams, and information system (IS) roll-out. In this paper we examine shifts over several years of globally distributed development and roll-out of an open source information system targeted at the public health care sector in developing countries, which touches on all three aspects. In following the development of an system as it co-evolved with the various institutional settings in which it was embedded, we highlight shifting sources of legitimation in institutional processes involved in health information systems implementation. The attention to changing sources of acceptance and legitimation frames our view on knowledge between local cultures and related stakeholders, in the interplay with global FOSS development.