Social movements have become central actors in the battles that are re-framing contemporary food markets in a variety of organizational and institutional configurations. With the aim of understand this process, this article contrasts the experiences of Nature & Progrès (France) and Ecovida Agroecology Network (Brazil). These movements are changing organic markets by means of Participatory Guarantee Systems (PGS), an innovative device created as a civic alternative to the conventional third-party audit. By crossing insights from New Economic Sociology and Social Movement Theory, we compare the two cases according to the social skills these movements have created to shape markets, including their alliances with State actors; the differentiated institutional contexts they face in each country; and the modus operandi established for each PGS. Results demonstrate that, while in both cases PGS has promoted a process of market re-institutionalization, Ecovida has been a more skillful actor in the market-making processes.