Résumé : Transparency is increasingly central to multilateral climate governance. In this article, we undertake one of the first systematic assessments of the nature and extent of compliance with transparency requirements under the United Nations Framework Convention on Climate Change (UNFCCC). Extensive resources are now being devoted to setting up national and international transparency systems that aim to render visible what individual countries are doing with regard to climate change. It is widely assumed that such transparency is vital to securing accountability, trust and thereby also enhanced climate actions from all. Yet, whether transparency lives up to this transformative promise remains largely unexamined. We generate a first systematic overview here of the nature and extent of country engagement with and adherence to UNFCCC transparency requirements. Drawing on extensive primary documents, including national reports and technical expert assessments of these reports, we generate ‘Transparency Adherence Indices’ for developed and developing country Parties to the UNFCCC. Our results reveal wide variations in adherence to mandatory reporting requirements and no clear general pattern of improvement since 2014. Our Indices help to illustrate trends and highlight knowledge gaps around the observed adherence patterns. This is timely since the 2015 Paris Agreement calls for an ‘enhanced transparency framework’ to be implemented by 2024 that builds on existing UNFCCC transparency systems. We conclude with identifying a research and policy agenda to help explain observed patterns of adherence, and emphasize the need for continued scrutiny of assumed links between transparency and climate action.