Sociolegal scholars have long debated the effectiveness of legal mobilization as a strategy for achieving social change. In addition to evaluating outcomes of wins and losses in court, they have identified several indirect effects of legal mobilization on social movements. Mobilizing new rights concepts can increase support for a movement, divide its base, and create new political allies or opponents. A win in court might lead to rights being institutionalized but not enforced, and it can serve to demobilize a movement base. This article contributes to this body of literature by arguing that movement groups can strategically mobilize the law to engage in co-optation from below – learning about an agency in order to build more effective organizing strategies. Using data gathered as a participant ethnographer in a grassroots environmental justice organization, I show how organizers used meetings with state regulators to learn how the agency interprets and enforces environmental laws and adjust their tactics in response. This study also demonstrates the value of conducting in-depth studies of local legal contests even as we seek to understand the role of the law in navigating our most pressing global challenges.