The notion of agency is a very complex one and has been used in the literature with a number of different meanings. In particular, starting from Giddens, it has increasingly been adopted to qualify any action performed by participants in communication. In this chapter, this paper will propose a specific interpretation of the concept of agency. Agency is seen here as a qualifying aspect not of any action, but in particular of those actions which have an impact on a social system by creating visible change. While both the notions of ‘being visible’ and ‘social change’ are complex ones in bilingual interpreter-mediated interaction, the main attempt of the paper will be to show, through examples from authentic interaction, that interpreters (and/or mediators) can visibly operate change in the structure of positioning in the interaction and possibly in the structure of roles in social systems, and thus exercise agency.