Westlaw is one of the primary online legal research services for lawyers and legal professionals in the United States and is a part of West. In addition, it provides proprietary database services. Information resources on Westlaw include more than 40,000 databases of case law, state and federal statutes, administrative codes, newspaper and magazine articles, public records, law journals, law reviews, treatises, legal forms and other information resources.

Most legal documents on Westlaw are indexed to the West Key Number System, which is West's master classification system of U.S. law. Westlaw supports natural language and Boolean searches. Other significant Westlaw features include KeyCite, a citation checking service, which allows customers to determine whether cases or statutes are still good law; and a customizable tabbed interface that lets customers bring their most-used resources to the top. Other tabs organize Westlaw content around the specific work needs of litigators, in-house corporate practitioners, and lawyers who specialize in any of over 150 legal topics. Most customers are attorneys or law students, but other individuals can also obtain accounts.