Abstract Climate Change Mitigation Technologies (CCMTs) are becoming increasingly more important, both politically and economically. Having recognized this, the EPO cooperated with the United Nations Environmental Program (UNEP) and the International Centre on Trade and Sustainable Development (ICTSD) and produced a study on Patents and Clean Energy. To consolidate the efforts invested in this study, the Y02 patent classification was created. This is a tagging scheme developed by experienced examiners working in the relevant fields, in cooperation with external experts, for patent documents related to CCMTs, which provides additional classification next to the regular ECLA and IPC classification of such documents. Patent documents were tagged by means of search strategies by experienced expert examiners, which were formalized into algorithms that can be re-run periodically to update the classes. Currently there are 2 subclasses: Y02C (for Greenhouse gas capture and storage) and Y02E (CCMTs relating to energy generation, transmission or distribution). At the time of writing, over 650,000 documents have been tagged with Y02 codes. A comparison between published patent documents with Y02 tags and published patent documents in general confirms that over the last 15 years the annual amount of patents related to “clean energy” has grown more than twice as fast as the average of all patents. The Y02 codes are available and searchable through Espacenet or PATSTAT.