We present a method how to estimate and compare the cooperative behavior of countries within the international climate change regime. Two indicators measure whether and how fast countries have committed to the United Nations Framework on Climate Change (UNFCCC) and the Kyoto Protocol (KP). Three additional indicators quantify whether and how effectively measures have been implemented in line with these agreements. These three measures are reporting, financial contributions, and development of per capita CO₂ emissions in relation to the per capita gross domestic product of each country. Results show that developed countries with emission targets under the KP ratified the protocol more often and faster, submitted their report timelier, and paid their annual financial contributions to the UNFCCC secretariat more regularly than the other countries. However, concerning CO₂ emissions, developing countries are evaluated more positively than developed countries. The five indicators are aggregated to a ‘Cooperation Index’ that evaluates 198 countries’ cooperative behavior within the international climate regime on a scale between 0 (=least cooperative) and 6 (=most cooperative). According to this Cooperation Index, the following large countries are ranked after their level of cooperation in ascending order: United States of America, Australia, Russia, Canada, Brazil, China, India, South Africa, and large European countries.