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. Print digests are available in the library. Westlaw also offers a searchable key number system, which can be accessed from the Tools tab on the homepage.
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:
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.
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 Tenant, Intoxicating 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.