USPTO Web Patent Databases
This full-text database created by the US Patent and Trademark Office, offers all US patents issued since 1790. Pre-1976 patents are searchable by patent number and pre-1976 classifications codes. Full-test images are available for the patents.
Google Patents
With Google Patents, you can search and read the full text of patent grants and applications from around the world. If you're looking for prior art, you can use the integrated Prior Art Finder tool and Google Scholar documents to find patent and non-patent prior art, all in one interface. Google Patents includes patent applications and grants from the USPTO, EPO, WIPO, DPMA, CIPO and SIPO. Patents without English full text are machine-translated to English, so you can search foreign patent documents using only English keywords. Documents from Google Scholar have been classified with Cooperative Patent Classification (CPC) codes using a machine-classification model, to make it easier to search non-patent literature in a patent searching context.
Espacenet
Espacenet is an online resource created by the European Patent Office. It includes patents issued by the European Patent Office, WIPO and a number of countries.