Non-state actors will play a unique and crucial role in the implementation of the Paris Agreement. Although much of the focus in the lead-up to Paris was on the mitigation commitments and actions of non-state actors, this essay focuses on another valuable contribution they can make: to hold the parties to their obligations under the Paris Agreement. I argue that, while the formal avenues for non-state-actor participation in review processes—encompassing the review of implementation, compliance, and effectiveness—remain limited, there are several other ways in which non-state actors can be, and already have been, influential.1