This chapter reflects on non-compliance procedures, which have emerged in multilateral environmental agreements (MEAs) as they have in other areas of international law. While the focus of international treaty negotiation may, at one point, have been the substantive issues, the scope has, over time, shifted to include efforts to ensure the effective implementation of the substantive commitments and obligations negotiated. Along with other elements, such as dispute settlement procedures, education, and capacity-building, non-compliance procedures have become a key element of the overall effort to ensure the effective implementation of MEAs. The chapter considers the role of compliance systems in MEAs, with a brief survey of the debate over the respective role of facilitation and enforcement, followed by an exploration of the relationship between the primary rule system and elements of the compliance system. It then looks at the key elements of compliance systems before studying a selection of MEA compliance systems.