Case Law Research Guide

This guide details how to read a case citation and sets out the print and online sources for finding cases.


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Using West Digests, Headnotes, and Key Numbers to Find Case Law

A digest helps you to find cases on a specific legal issue or topic. West digests use headnotes and key numbers to organize and summarize all cases by subject. 

West print digests are available in the library. Westlaw offers a searchable key number system, which can be narrowed by topic to a list of headnotes, serving as the equivalent of a digest in print.

Lexis uses headnotes and Lexis Topics, a classification system with its own set of topics and subtopics that functions similarly to help you find cases on a specific legal issue.

What is a Headnote?

Before a case is published in a reporter, an editor at West reads the case and selects the important issues of law. For each major issue, the editor then writes a short description called a headnote. These headnotes are typically found at the beginning of each opinion and help the reader quickly determine the issue(s) discussed in the case. For example, here is the third headnote of a U.S. Supreme Court opinion, Gideon v. Wainwright, 372 U.S. 335, on Westlaw:

The headnote describes one major issue in the case: whether an indigent defendant in a criminal prosecution in state court has the right to have counsel appointed for him. The broad topic assigned is Constitutional Law, which is assigned topic number 92. The subtopic is Appointment of Counsel, which is assigned key number 4809.

Gideon v. Wainwright, 372 U.S. 335, on Lexis also offers headnotes at the top of the case. Because they are written by LexisNexis attorney-editors, LexisNexis headnotes are not the same as West headnotes.

What is a Key Number?

When writing the headnotes, the West editor gives each one a headline (broad topic) selected from a list of about 450 possibilities. Some examples are Landlord and TenantIntoxicating Liquors, and Automobiles. Finally, the editor will assign the headnote a specific subtopic, such as Injury to Tenant or Occupant. In West digests, this subtopic is represented by a number called a key number.

In the example above, within the topic Constitutional Law, the key number for Appointment of Counsel is 4809. Each topic and key number combination represents a unique point of law. Key numbers are the same in all West digests for all jurisdictions; therefore, you would use the same topic and key number, Constitutional Law 4809, to find cases in a specific jurisdiction, e.g. Massachusetts, addressing the same topic as the Supreme Court case above.

After finding a useful headnote at the top of a case on Westlaw, click into a relevant key number next to the headnote, and then search or narrow by jurisdiction as needed to identify relevant cases.

Similarly, if you're using Lexis Topics, after finding a useful headnote at the top of a case on Lexis, click into a relevant topic above the headnote, and then search or narrow by jurisdiction as needed to identify relevant cases

Using Headnotes Tutorial