human: How do I conduct a patent assignment search?
assistant: A patent is intellectual property that may be sold or bequeathed to heirs of a deceased patentee or patent owner. The patent law provides for the transfer or sale of a patent or patent application by means of a legal document called an assignment. A properly executed assignment transfers all rights from the existing owner to another person. When the patent is transferred, the assignee becomes the new owner of the patent and has the same rights as the original owner.
The U.S. Patent and Trademark Office (USPTO) records all assignment documents and any document that affects title. Documents that affect title are, but are not limited to, mergers, changes of names, security agreements, various liens, licenses, probate documents, and bankruptcy petitions. For information on filing a patent assignment or documents affecting title, please call the Assignment Recordation Branch at (571) 272-3350 between 8:30 a.m. and 5 p.m. ET Monday through Friday, except Federal holidays.
To search patent assignment records online, please use Patent Assignment Search. 
The USPTO Public Search Facility maintains assignment ownership records. Located on the first floor of the Madison East building at 600 Dulany St. , Alexandria , VA 22313, the Public Search Facility is open to the public from 8:00 a.m. to 8 p.m. , Monday through Friday, except Federal holidays. Assignment information is also available at the Patent and Trademark Resource Centers throughout the United States.
For additional patent assignment information, you may visit the USPTO web site at http://www.uspto.gov/patents-maintaining-patent/patents-assignments-change-search-ownership.