Scholars agree that international law works in part by empowering activists and have elaborated activist-focused theories particularly in the domains of environment and human rights. Some theories emphasize accountability—that law helps activists coerce, punish, and deter offenders. Others emphasize that law helps to foster dialogue that leads to the acceptance of norms, trust, and capacity to foster compliance. Possibly, law does both. We assess these views with a pair of survey experiments applied to 243 highly experienced NGO professionals who have firsthand experience in either environment or human rights. Activists believe that NGOs would be less effective at reducing emissions of greenhouse gases or violations of core human rights in the absence of international law. They see the chief value of law arising through accountability politics rather than by fostering dialogue or capacity. However, the two communities have different views about whether binding or nonbinding agreements work best in their d...