Prepared by Elisabeth Lindsay.
Boolean refers to a system of logic devised by English mathematician George Boole to increase the effectiveness of a computer search. The Boolean "operators" (AND, OR, IF THEN, EXCEPT and NOT) can be used in combination with other words and phrases to broaden or narrow computer searches. Virtually all computer search engines and databases support the Boolean search method.
Most genealogists utilize the Boolean search method, often without even realizing it, as the AND operator is generally employed by default whenever two or more keywords are entered into a search. Many search engines and databases offer an Advanced Search feature allowing users to specify words or phrases to be included or excluded from a search. Boolean search operators can be used in combination with a wildcard to further limit and refine search results.