This article analyses the governance of VET for adults and its development from a historical-institutionalist perspective. It takes a look at the collective skill formation system of Switzerland, in which the federal government and private companies (or the associations representing them) play integral roles. The article argues that the establishment of VET for adults is a form of policy expansion, in which certain actors -- especially from the canton administrations -- exert considerable influence in the initial phase, but then get side-lined as the governance structure and institutional framework of formal VET shape the process of expansion, due to numerous feedback mechanisms. These findings are relevant not only for understanding the development of VET for adults, but also for a more general understanding of educational reforms that affect other policy fields.