The Paris Agreement establishes an “enhanced transparency framework” to build mutual trust and confidence and to promote effective implementation. This framework combines common reporting and review requirements for all parties with “built-in flexibility” for developing countries. The agreement requires that parties, in elaborating the operational details of the transparency framework, build on experience with existing transparency arrangements under the U.N. Framework Convention on Climate Change (UNFCCC). Over the past year, developed and developing countries have shared their experiences with the existing transparency system in a variety of public forums. This brief highlights key lessons learned that can help inform the design of the Paris transparency framework.