A patent for an invention is the grant of a property right to the inventor. Generally, the term of a new patent is 20 years from the date on which the application for the patent was filed in the United States. There are three types of patents: (1) Utility, covering function; (2) Design, covering ornamental design; and (3) Plant, for a new variety of plant.
Google Patent Search
Google Patent Search covers United States and world patents.
European and World Patents (espacenet)
The espacenet system is a searchable collection of of patent documents published around the world. English-language abstracts are usually available from 1970. Full text documents are provided if available.
USPTO Patent Database
The U.S. Patent and Trademark Office (USPTO) database includes full-page images beginning with the first U.S. patent issued in 1790. Issued patents starting from 1976 and patent applications are fully searchable. Patents issued between 1790 and 1975 are only searchable by the patent number or current U.S. classification.
Derwent Innovations Index
This resource includes value-added patent information and patent citation information. You can use additional descriptive information and coding to quickly understand a patent's significance and its relationship to other patents. Coverage from 1963 to present.
The Cooperative Patent Classification (CPC) scheme is a partnership between the United States Patent and Trademark Office (USPTO) and the European Patent Office (EPO) to harmonize their existing classification systems. While it is possible to search patents using keywords, the best way to conduct a comprehensive patent search is by classification. Classification brings together similar concepts when different terms have been used to describe them. If you do not know the proper classification number, you can browse the CPC. Alternatively you can start with a keyword search in a patent database such as Google Patents, find a relevant patent and look at the cooperative classiifications numbers assigned to the patent.
PatentsView is a patent data visualization and analysis tool intended to increase the value, utility, and transparency of US patent data. For example, you can see all of the patents for which Yale University is the assignee along with which patents are most frequently cited, top inventors, etc. Try a search for "Yale University" in the assignee field.