Tertiary sources are publications that summarize and digest the information in primary and secondary sources to provide background on a topic, idea, or event. Encyclopedias and biographical dictionaries are good examples of tertiary sources.
Access Science. [New York]: McGraw-Hill.
American National Biography. [New York]: Oxford UP, 2000- .
International Encyclopedia of the Social & Behavioral Sciences. 2nd edition. Amsterdam: Elsevier, 2015- .
New Dictionary of the History of Ideas. New York: Oxford UP, 2013.
The Oxford Encyclopedia of American Military and Diplomatic History. New York: Scribner, 2005.