Patent documents are categorized using the international patent classification (IPC) and some national and regional classification systems, including the European classification scheme (ECLA). In addition to the basic bibliometric and legal data, the database also includes patent descriptions (abstracts) and citation data. The relevant inventions have been identified using specially developed tagging codes for climate change mitigation technologies (see Table 4.1). This tagging scheme (Y02) has been developed by a team of patent examiners at the European Patent Office, with inputs from collaborating researchers (including the authors) and has now been implemented into the ECLA system.