Boolean Operators link concepts and are used to broaden or narrow your search.
AND - finds results with your all search terms. AND narrows your search.
OR - finds results with any of your search terms. OR broadens your search.
NOT - finds search terms only before the NOT. NOT narrows your search.

Many databases have an Advanced Search option with a pull down menu that allows you to choose a Boolean operator and a Field Type, such as Title or Author. When searching a database using your own search strategy, the Boolean terms must be capitalized.