When should you use quotation marks in a search query?
On Westlaw, you must use quotation marks around phrases of two or more words, whether you are doing a "Terms and Connectors" search or a "Natural Language" search. Example: "fourth amendment". With the quotation marks, Westlaw will only retrieve documents in which "fourth amendment" appears as a phrase, both words in that order with no words between them. Without the quotation marks, Westlaw will treat the words as individual search terms. If you are researching the Fourth Amendment, you would not want to be inundated with cases in which either "fourth" or "amendment" occurs.
On LexisNexis, you need to use quotation marks around phrases in "Natural Language" searches, but not in "Terms and Connectors" searches. If there is no connector, such as AND or OR, between two search terms in a "Terms and Connectors" search, LexisNexis will search for the terms as a phrase. However, it does not hurt to use quotation marks around phrases in "Terms and Connectors" searches on LexisNexis. Since you do not know whether your next employer will have Westlaw or LexisNexis, using quotation marks around phrases even in LexisNexis "Terms and Connectors" searches will help you stay in the habit of using them for phrase searches. Then, if you find yourself working somewhere that only has Westlaw, you will already be comfortable with the search language.
Most search engines, including Google, Yahoo! and Teoma, will also accept quotation marks to indicate a phrase. Click on Help or Tips at your search engine to find out if your search engine accepts quotation marks.
Update: Several Lawyering Skills students pointed out that both Westlaw and LexisNexis require quotation marks around phrases in their "Natural Language" searches. I have modified the above post to include "Natural Language" searches.