Tracking progress in the transition to low-carbon energy systems, including action taken through countries’ Nationally Determined Contributions (NDCs), is necessary to focus attention on the steps needed today to achieve both short- and long-term climate goals. United Nations climate agreements have so far focused tracking efforts on greenhouse gases: while this is critical, tracking greenhouse gas targets alone cannot reveal whether change is occurring rapidly enough in underlying energy infrastructure. This document presents some metrics which the IEA believes are important in tracking energy sector decarbonisation. However, an even wider suite of energy metrics should be used to inform the international climate policy process and the development of national action plans. These include tracking renewable energy deployment, energy efficiency improvements and low-carbon investments. The IEA aims to contribute to the development and implementation of such metrics moving forward.