Article 15 of the Paris Agreement establishes a mechanism to facilitate implementation of and promote compliance with the provisions of the Paris Agreement. Along with the global stocktake and the transparency framework, this mechanism provides a means of assessing and enhancing the effectiveness of parties’ efforts toward the agreement’s long-term goals. Article 15, and the decision adopting the Paris Agrement, provide some guidance on the mechanism’s design and operation. But important aspects—including how the mechanism would be triggered and the outcomes it could produce—are among the issues to be addressed in 2018 when parties adopt detailed implementing guidance for the Paris Agreement. This brief identifies key overarching considerations, and explores the range of issues and options that have emerged with respect to specific elements of the mechanism’s design and operation.