Databases from the U.S, Patent and Trademark Office (USPTO)
1. Patent Public Search (NEW as of February 2022!) : Searches both U.S. patent grants and published U.S. patent applications.
2. PatFT and AppFT (Classic databases; will remain available until the end of September 2022. Patent Public Search is recommended over PatFT/AppFT): Use PatFT to search for U.S. patent grants, and AppFT to search for U.S. patent applications. Note that PatFT only allows for full-text searching back to 1976; to find patents granted before then, you must search by classification.
Browse or search the Cooperative Patent Classification (CPC) database to find relevant classification schemes.
The worldwide database (from the European Patent Office) contains information on published patent applications and granted patents from over 100 patent-granting authorities. Can machine-translate patent documents.
Allows for full-text searching of patent grants and applications from the United States and from 100+ patent offices around the world.
The PATENTSCOPE database provides access to international Patent Cooperation Treaty (PCT) applications in full text format on the day of publication, as well as to patent documents of participating national and regional patent offices.
The USPTO's Patent and Trademark Resource Center (PTRC) provides a CBT (computer based training) tutorial with a detailed review of how to conduct a preliminary U.S. Patent Search. This updated tutorial covers searching using the new Patent Public Search database, and talks about searching by Cooperative Patent Classification (CPC).