The emergence of a regional business organization in Brittany in the latter half of the 20th century raises questions about traditional analyses of employers' organizations that stress the determinative impact of macro-institutions (the State, markets). Based on a neo-institutionalist perspective, this article emphasizes the role of collective action in the formation of an employers' group and the combination – varying over time – of two mechanisms of institutionalization (political and economic). Amid economic internationalization and the withdrawal of the State, this new form of regionalism is key to a reassessment of collective and bottom-up dynamics in the crystallization of regional political orders.