Westlaw vs. Lexis: What's the Difference?

Start with what is the same. Both databases contain every published federal and state appellate opinion, both have the U.S. Code and all fifty states' codes, both have the Code of Federal Regulations and the Federal Register, and both carry enormous volumes of unpublished trial court opinions. If your assignment is "find the leading Second Circuit case on X," you will find it on either. Anyone who tells you one platform 'has more law' is describing a marketing claim, not your research problem.

The differences are in the editorial layer that sits on top of the law and in the licensed content each company owns. Thomson Reuters publishes the National Reporter System (F.4th, N.E.3d, S.W.3d, and so on), so West's editorial apparatus—synopses, headnotes, Key Numbers—is native to Westlaw. LexisNexis owns Matthew Bender, the largest stable of practitioner treatises, plus Law360 and the Nexis news archive. Those ownership facts drive almost every practical difference you will notice.

One more real difference: each platform assigns its own unique citation to unreported opinions. Westlaw uses 2024 WL 1234567; Lexis uses 2024 U.S. Dist. LEXIS 12345. Under Bluebook Rule 10.8.1(a), you cite an unreported case to the database you actually used, with the docket number and full date—for example, Smith v. Jones, No. 22-cv-4501, 2024 WL 1234567, at *3 (S.D.N.Y. Mar. 4, 2024). You cannot swap a WL cite for a LEXIS cite without pulling the case up on the other service and finding the corresponding star page.

Both citators do the same job—tell you whether a case is still good law and who has cited it—but the symbols are different and you must not confuse them. KeyCite on Westlaw uses a red flag (the case is no longer good law for at least one point), a yellow flag (some negative treatment, but not overruled or reversed), and a blue-striped flag (an appeal is pending). Westlaw's newer platforms also add an orange 'overruling risk' warning, which flags a case that relies on an authority that has since been overruled, even though the case itself has no direct negative history.

Shepard's on Lexis uses a red octagon/stop sign (strong negative treatment such as overruled or reversed), an orange square with a Q (validity questioned by citing references), a yellow triangle (possible negative treatment—criticized, limited, distinguished), a green diamond with a plus (positive treatment), and blue circles for neutral citing references. There is no perfect one-to-one mapping between the two systems, which is exactly why serious researchers run both when the stakes are high.

The rule that matters more than the symbols: a flag or a stop sign never tells you not to use a case. It tells you to read the citing reference. A red flag may reflect reversal on an issue you do not care about. A clean green case may have been quietly gutted by a later decision that never says 'overruled.' Click through, read the treatment, and note the point of law involved.

West's Key Number System is the older and more structured of the two. West editors write headnotes in their own words and file each one into a hierarchical taxonomy of roughly 400 topics subdivided into Key Numbers. Because every case in the National Reporter System has been classified this way since the nineteenth century, clicking a Key Number gives you a curated list of every case in any jurisdiction that a West editor thought stood for that proposition. This is the single most powerful feature Westlaw has, and it is why many research professors teach Westlaw first.

Lexis headnotes are drawn verbatim from the language of the opinion itself, then linked into Lexis's own topic hierarchy. The advantage is fidelity—you are reading the court's actual words, not an editor's paraphrase, which is safer when you plan to quote. Lexis also lets you Shepardize a single headnote, which narrows a citator report to the one issue you care about, and 'more like this headnote' finds passages with similar language.

Practically: use Key Numbers when you want comprehensive coverage of a settled doctrine across jurisdictions. Use Lexis headnote tools when you have one good case and want to trace one specific holding forward.

This is where the choice can actually decide your research. Westlaw exclusively carries American Law Reports (A.L.R.), Corpus Juris Secundum, American Jurisprudence 2d, Wright & Miller's Federal Practice and Procedure, McCarthy on Trademarks, and the Rutter Group California practice guides. Lexis exclusively carries the Matthew Bender library, including Collier on Bankruptcy, Moore's Federal Practice, Nimmer on Copyright, Chisum on Patents, and Weinstein's Federal Evidence, plus Law360 and the Nexis news and business archive.

If your seminar paper is on bankruptcy priority, you want Collier, which means Lexis. If you are surveying how jurisdictions have split on an odd tort question, an A.L.R. annotation will save you a week, and that means Westlaw. Check the secondary source you need before you pick a platform for a big project, not after.

Some state-specific and jurisdictional materials are also uneven. Older state administrative materials, municipal codes, and certain court records appear on one service and not the other. When coverage matters, read the database's scope or coverage note rather than assuming.

Both accept natural-language queries and both accept Boolean terms and connectors, but the connector vocabulary differs enough to trip you up. Westlaw uses & for AND, /s and /p for same sentence and same paragraph, /n for within n terms, +n for preceding within n terms, and % for BUT NOT. Lexis uses AND, w/s, w/p, w/n, pre/n, and AND NOT. Both use ! as a root expander (neglig! catches negligent, negligence, negligently) and * as a single-character wildcard, and both treat quoted text as a phrase.

Field and segment restrictions differ in name. On Westlaw you restrict by field—ti(marbury) for the case title, ju() for judge. On Lexis you restrict by segment—name(marbury), writtenby(), judges(). Same concept, different label, and the platform's help screens list the current set.

Both companies have built generative AI research assistants into their premium platforms, and both have litigation analytics that profile judges, courts, and opposing counsel and estimate timelines and outcomes. Feature names and student access change every academic year, so ask your school's Westlaw and Lexis representatives what your account actually includes rather than relying on a guide.

Treat AI answers as a starting lead, never as authority. Every generative tool can misstate a holding or attribute a proposition to the wrong case. Verify anything the tool tells you by opening the opinion and running the citator yourself. Lawyers have been sanctioned for filing briefs containing fabricated citations produced by AI tools; the same standard will apply to your memos and your bar admission character review.

For dockets and filings, note a third option: Bloomberg Law includes broad docket access in its flat subscription and has its own citator, BCite. Many law schools give students Bloomberg Law accounts alongside Westlaw and Lexis, and it is often the fastest route to complaints, briefs, and transactional documents.

Learn both, but go deep on one. In law school you have free, unlimited academic access to both platforms—the only time in your career that will be true. Employers do not care which you prefer; they care that you can find the answer on whatever they subscribe to. Large firms often have both. Small firms, solos, and government offices frequently have neither and use lower-cost services like Fastcase/vLex or Casetext instead, so keep your terms-and-connectors skills platform-agnostic.

Be careful about the terms of your student access. Academic passwords are licensed for coursework, and both companies restrict use for paid work such as a summer associate position or a clerkship. If you need research access for a paid job, ask the employer for their credentials. Both companies also run graduate access programs that extend limited use for bar study and job searching, but the hours and duration change annually—confirm the current terms with your law librarian before you graduate.

One last habit: whichever platform you use, always finish by running the citator on every authority you cite. That step is not optional, and it is the one thing a supervising attorney will check first.