IET 317: Edmonson

A patent is a set of exclusive rights which has been granted by a sovereign state (or sometimes as intergovernmental organization). Such rights are granted to an inventor, for a limited duration, in exchange for a detailed public disclosure of such invention. Patents typically exclude others from making or offering for sale those inventions.

Patents are generally granted from specific countries. Patent numbers often have prefixes that indicate which country granted the patent. For example, the patent US5577561A was generated from within the United States. Follow this link for a list of country codes. That said, you may also encounter patents that have been generated from the World Intellectual Property Organization (WIPO) which is an organization created by the United Nations in 1967.

Derwent Innovations Index (Web of Science) - Provides access to over 15,000,000 patents with links to cited and citing patents, cited articles, and (some) full-text patent data sources. Divided by Chemical, Electrical and Electronic, and Engineering.

United States Patent and Trademark Organization (USPTO) - Includes full text of U.S. patents and patent application information. 

European Patent Office Espacenet Patent Search - Provides full-text access of published European patents. Includes over 100 countries. 

Google Patent Search - Not particularly comprehensive but Google does provide many full-texts of patents

World Intellectual Property Organization (WIPO) - Searches over 69 million international and national patent documents. Includes more than two million published international patent applications (PCT). WIPO is affiliated with the United Nations.