A patent classification is a way the examiners of patent offices or other people arrange documents, such as patent applications, disclosing inventions according to the technical features of the inventions. They arrange documents using a patent classification so that they can quickly find a document disclosing the invention identical or similar to the invention for which a patent is claimed. The same document may be classified in several classes.
A patent classification is fixed under an agreement among people, otherwise it is useless. The International Patent Classification (IPC) is agreed internationally. The United States Patent Classification (USPC) is fixed by the United States Patent and Trademark Office (USPTO). The European Classification (ECLA) is based on the IPC but adapted by the European Patent Office (EPO) to its own requirements. The Derwent classification system is fixed by an enterprise.
In October 2010, the EPO and USPTO launched a joint project to create the Cooperation Patent Classification (CPC) in order to harmonise the patent classifications systems between the two offices.