Fifty years ago, when the nation’s appellate judges and their law clerks researched an issue and cited authority on a point, they worked from and referred to books drawn from a library shelf. Today, although their many citations employing volume and page numbers evoke that era, judges and those who support them are, nearly always, drawing upon one of two comprehensive digital collections of caselaw, statutes, and commentary, Lexis or Westlaw. In some jurisdictions subscriptions to both services allow individual judges to choose between them. That is true of the federal judiciary and many state courts, as well. Some states, however, contract with only one of the competing offerings. (For background on this point, see How State Courts Contract for Online Legal Information.)
Which of the two digital law libraries, a court or individual judge employs leaves a marker, akin to DNA, in some of the decisions they write. As a consequence, it is possible to investigate these two systems’ respective shares of judicial use. The telltale trace is left whenever a judge cites a decision that has not yet been (and may never be) compiled into a numbered and paginated volume. Lexis and Westlaw provide distinctive, proprietary schemes for citing such cases. The Lexis document identifier includes the term “LEXIS”; Westlaw’s, “WL”. A search for those unique character strings in a court’s opinions (while still in the form of their initial release and before they have been added to and altered by either commercial system) reveals their authors’ data source.
Such a search is possible on the Courtlistener database maintained by the Free Law Project (www.courtlistener.com). A Courtllistener search of the 2025 decisions released by the U.S. Supreme Court and Circuit Court of Appeals, as well as those of all state courts of last resort, reveals the following:
- During 2025 the justices of the Supreme Court included numerous “WL” citations in their opinions but not a single “LEXIS” case reference. Despite their many substantive disagreements, all nine justices appear unanimous in a preference for Westlaw.
- Roughly two thousand 2025 decisions by U.S. Court of Appeals judges cited to Westlaw, fewer than one hundred to Lexis. (Names can be named. Judge Frank Easterbrook of the 7th Circuit appears to be a committed Lexis user.)
- Among the 2025 decisions rendered by state courts of last resort, “WL” appears in over one thousand, “LEXIS” in fewer than one hundred. The only significant “LEXIS” totals appear in decisions from the supreme courts of Montana and Virginia.
Unfortunately, Courtlistener’s collection of recent U.S. District Court decisions is insufficiently complete for it to be used for a comparable survey. However, the way Westlaw and Lexis treat judicial citations that employ the other’s proprietary scheme makes it possible to turn their own systems to this purpose.
Westlaw does not insert parallel LEXIS citations for WL citations when the opinion author has not provided them. Consequently, a Westlaw search of 2025 U.S. District Court opinions for the term “LEXIS” furnishes a rough measure of Lexis use by district court judges. Such a search yields a count of 1,438 decisions. An identical search on the term “WL” retrieves a larger number than Westlaw will total.
Tellingly, Lexis does add parallel “LEXIS” cites to all those in which a judge has employed a Westlaw “WL” designation. Consequently, a comparable pair of searches on Lexis produces meaningless results. However, when a judge’s Westlaw citation includes a star-page pincite, Lexis is unable to provide its equivalent. A Lexis search designed to retrieve 2025 U.S. District Court opinions containing a WL citation followed by a star-page pincite generates a total of over 90,000. A comparable search for LEXIS citations with star-page pincites returns fewer than one-sixth that number.
In conclusion, citation analysis using both Westlaw and Lexis reveals that, just as is true with other U.S. courts, when doing caselaw research a large majority of U.S. District Court judges use Westlaw.