Does international law matter on the periphery, where potential subjects are marginalized with uncertain legal status and without lawmaking power? Under what conditions would international law matter among the actors on the periphery, to be accepted as law, remain relevant, and eventually be complied with? By adopting an interdisciplinary perspective from international law and international relations, this article assesses how international humanitarian law (ihl) is accepted and adhered to among the non-state armed actors (nsaas). The author argues that international law matters on the periphery when two conditions are met. The first is when incentives of nsaas are compatible with ihl’s goal of restraint. The second is when the interpretation of ihl at the local level is consistent with international law at the global level. This article provides ample examples of nsaas’ words and deeds to illustrate the arguments.