The technological innovation system (TIS) concept has established a strong tradition in analyzing emerging environmental industries. Despite the growing evidence of globalization of innovation activities, TIS literature has so far mostly focused on nationally bound systems. The present paper proposes an analytical framework for assessing the international dimension of TISs by adopting a relational view on actors and networks. Social network analysis provides indicators for specifying the errors which spatially "containerized" TIS studies are likely to commit. The framework is applied to a co-publication dataset on membrane bioreactor (MBR) technology, which reveals a strongly international and multi-scalar TIS structure. The findings suggest that the definition of spatial boundaries deserves much more attention in innovation studies. Economic geographers could play an important role in developing the concepts needed.