Skip to Main Content

Case Finding and Advanced Searching Strategies


The West Key Number System is a classification system of U.S. law that indexes cases into over 400 topics and more than 98,000 legal issues.  Westlaw assigns a topic and key number to each legal issue within a case.  The West Key Number System allows you to efficiently find other cases addressing your legal issue in any jurisdiction because all federal and state cases included in the system are organized using the same topics and by the same points of law.

Using the West Key Number System is particularly useful when you have identified a relevant case and would like to find additional cases addressing a certain point of law or legal issue from other jurisdictions.

A key number consists of a topic number, followed by a number to identify the issue within that topic.  For instance, 349k28 is referring to the topic of Searches and Seizures (349) and the issue of abandoned, surrendered, or disclaimed items (k28).  The image below shows this topic's place in the Key Number System's hierarchy.  The topic of Searches and Seizures contains the subtopic In General, which contains the subtopic Persons, Places, and Things Protected, which includes, among others, the subtopic of Abandoned, surrendered, or disclaimed items.

Screenshot from Westlaw showing Key Number hierarchy for 349k28

Note: This strategy is only for conducting case law research on Westlaw.  Lexis does not have a similar, comprehensive digest system, though it has started to develop a Legal Topics system.


You can also browse the topics in the West Key Number System by clicking on "Key Numbers" on Westlaw's homepage (or if you type in West Key Number System in the search bar, it should appear as a suggested option).  Please note that browsing for key numbers is generally not as efficient as entering into the West Key Number System from a relevant case. 

Screenshot showing top-level Key Number topics

You will then find a list of topics.  You can click on "Patents," for example, to get to a page with the outline structure for this topic, including many sub-topics and sub-sub-topics.

Screenshot showing "Patent" topic's page, with outline of sub-topics

You can expand sections to see more details, including Key Numbers.  You can also search for Key Numbers relevant to your issue based on the search terms.  Alternatively, in the main search bar, you can conduct keyword searches across the content of the West Key Number headnotes.  For more information on headnotes, please see the Headnotes section of this guide. 

Screenshot highlighting different search bars: the main searchbar at the top of the page for searching West Key Number Headnotes, and the searchbar just above the list of topics for searching across Key Number topic names

If you conduct a search for key numbers relevant to your issue, Westlaw will translate terms and connectors queries into plain language/natural language search terms, so you need not run elaborate terms and connectors searches here. 

Screenshot showing results for searching "money laundering" across Key Number topics

Accessing Key Numbers from a Case

The West Key Number system works in conjunction with headnotes.  West editors identify the legal issues in cases and discuss each issue in a headnote.  Headnotes are numbered so you can use them as you would a table of contents to a case; you can click on the number to go to the spot in the text where that issue is discussed, and or click on the corresponding number in the text to go back to the headnote.  West editors then assign each headnote one or more topics and Key Numbers.  If you have identified a relevant case, you can use the Key Number System to find other cases addressing the same legal issues.

Here is an example of a headnote in Westlaw (headnote number 3 in the case).

Screenshot of Westlaw page for United States v. Johnson, 874 F.3d 1078, showing Headnote 3 on Obstructing Justice

Numbers corresponding to the headnote numbers then appear inside brackets within the text of the opinion.  For example, here is the text that corresponds to headnote 3 in the opinion.

Screenshot of Westlaw page for United States v. Johnson, 874 F.3d 1078, showing case text corresponding to Headnote 3

Immediately following the headnote number is the broad legal topic under which a West editor has classified that particular headnote.  Each of the 400+ legal topics that West attorney-editors have identified has a unique number.  In the example, the broad legal topic for headnote 3 is "Obstructing Justice," which is topic number 282.

Screenshot showing Key Numbers assigned to Headnote 3, listed to right of headnote

Listed under each broad legal topic are narrower subtopics.  In this example, the subtopics are: "Offenses Relating to Witnesses or Potential Witnesses" and "Tampering in general" and the Key Numbers are 282k134 and 282k136, respectively.

Screenshot highlighting sub-topics in list of Key Numbers next to headnote

Clicking on 282k134, for example, will pull all of the cases that West editors have deemed relevant to the legal topic of obstructing justice, specifically on the issue of offenses relating to witnesses or potential witnesses.  Note that by default, you'll only be shown cases from the same jurisdiction as your original case.  If you want to browse cases in that key number from other jurisdictions, you can change the jurisdiction using the "Change" link above the list of cases.  You can also narrow your results within your selected jurisdiction(s) using the filters on the left-hand side. 

Screenshot of Westlaw showing list of cases under Key Number 282k134, highlighting jurisdiction filters in the left sidebar

You can further refine your results by using the filtering options in the left sidebar.  The "Search within results" option only searches across the headnotes, not the full-text of cases.  Use this function to narrow the headnotes to those that contain a specific keyword(s).  If you have retrieved too few cases, you can work your way up the West Key Number System to find cases classified under the broader issues.

Accessing Keys Numbers from a Secondary Source or Annotated Statute

If you have located a secondary source on point, you can utilize references to Key Numbers to pull cases on a particular legal issue of interest.  

For example, if you were researching the statutory provisions concerning patents and came across 69 Corpus Juris Secundum § 9, then you would find a reference to the Key Number System before the section's actual text:

Screenshot from Westlaw showing Key Number references above section text