Skip to main content

Legal Research

Fundamentals of Legal Research

Using key numbers to find cases

West was a dominent print publisher of case reports and developed its Digest keynumbering classification system over a hundred years ago. This is one of the big reasons that Westlaw is often preferred over other providers. If you use Westlaw for case research, you should be using its classification system.

You can find a West Key Number that is specific to your topic and then use it to find other cases with that Key Number.

Two ways to find them!

1.  Find a Key Number in one good case and click on it find additional cases in your desired jurisdiction.

2.  Click on West Key Number System from the landing page and then search or browse for relevant Key Numbers.  Once you find one, click on it to search for cases in your desired jurisdiction.



Mr. West published thousands of cases in his National Reporter System so cases from all jurisdictions were available for the first time. With all the cases out there he had to develop a method to find cases on a specific topic.

In 1848 West developed a classification system called the West Digest System to assist researchers in finding case law. The West Digest System is composed of topics and Key Numbers.

He decided that all legal issues fall into one of 414 broad topics. Each topic is divided into numerous subtopics.


Automobiles is one such topic. We can look at all the Key Numbers under the topic to find the one that is most specific to the issue of liability when items fall from a motor vehicle. Then, we can use it to find North Carolina cases on the topic. (Note: Most unpublished memorandum decisions do not have headnotes and Key Numbers.)

48AKey Number Symbol180. Instead of drawing a key shape, we use a "k" to represent the West Key: 48Ak180

48AVInjuries from Operation, or Use of Highway
48AV(A)Nature and Grounds of Liability
48Ak180Articles Projecting, Falling, or Thrown from Vehicle

Key Number Classifications

Okay, West developed a classification system with number topics and subtopics.  What next?

This Westcast podcast highlights the behind-the-scenes work at West to post, fact-check, headnote, and classify a U.S. Supreme Court case.


New Supreme Court case involving liability for operation of a motor vehicle.

Step 1:  A West editor reads the new opinion.

Step 2:  The editor summarizes each legal issue in a headnote.

Step 3:  The editor looks through the 415+ topics (and subtopics) to find the most relevant Key Number (of the over 90,000 available)

Step 4:  The most relevant Key Number is assigned to the headnote.

Step 5:  This Key Number can be used to find additional cases about the same issue.