Classification of Patents
A patent classification is the categorisation that allows patent offices, and all those who wish to search for a pending or granted patent, to find patents using a code system. Classification is according to the field of technology to which the invention relates and also what language the patent is written in. This speeds up the search for documents considerably.
Here you can find a list of patent databases:
USPTO patent databases - issued US patents and published applications (keyword searchable for patents after 1976 and all published applications)
Google Patents (beta) - US patents, keyword searchable back to 1789 although less reliable the further back you go.
Delphion - US, PCT, Japanese and European patents
Espacenet - the European Patent Office database
Further information on International Patent Classification can be found on the World Intellectual Property Organization website
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