The United Nations Climate Change Conference in Cancún is an opportunity for concrete progress in the international climate change effort. Key elements of success in Cancún include: 1) operational decisions improving the transparency of countries’ actions, and strengthening support for mitigation and adaptation in developing countries; and 2) a clear declaration by parties that their longer-term aim is a legally binding outcome. A Cancún agreement also should reflect individual country pledges and incorporate the temperature and finance goals of the Copenhagen Accord.