This article addresses the institutional scaling of information systems through the interplay of globally distributed free and open source software development with organizational processes. Through examining various phases of a long term project to implement information systems for the public health care sector in resource-poor countries, we highlight changing sources of acceptance and legitimation. The analysis centers on the balance between local and global levels, from pilot sites, through an emerging broader organizational field, to increasingly involving national level institutional settings. In parallel to the established view of the scaling of ICT implementations as relating to complexity and risk in the form of unintended side-effects of the growth of a system, the authors highlight the qualitative switch between regulatory contexts. Shifting relations to local institutions means that scalability requires actors to interact with quite different organizational cultures, accountabilities and communicative practices.