Boolean logic is an algebra that permits operations on sets of terms. Principal Boolean operators are AND (intersection), OR (union), and NOT (difference).

- ORUse OR to broaden the search strategy; each document must contain at least one of the terms connected by OR.

- ANDUse AND to narrow the search strategy; each document must contain all of the terms connected by AND.

NOTUse NOT to eliminate a term from the search strategy; each document must not contain the term following NOT.