Accounting rules and procedures will dictate how progress is tracked for various possible types of mitigation contributions that might be included in the 2015 agreement and how their achievement will be determined. Without such rules, it will be difficult, if not impossible, to accurately track progress toward individual contributions as well as towards limiting warming to 2° C or below. The report explores the components of a robust and rigorous accounting framework, lessons learned from existing accounting frame-works, and how such a framework can be developed for the 2015 agreement. The objective is to support the establishment of a sufficiently robust and rigorous common accounting framework for the 2015 agreement, including accounting rules for international transfers of units from marketbased mechanisms and the land sector.