West (Thomson Reuters) is one of the major legal publishers in the United States. West's digests are helpful for locating decisions relevant to a particular topic. Federal, state, and some regional and topical digests are available.

Digests are organized by topic and contain brief summaries of a decision's main issues. West calls its issue summaries Headnotes. In West's digest system, any given Headnote will be classified according to West's Key Number System.

The Key Number System categorizes the law into approximately 400 topics, and each topic is further subdivided into Key Numbers (there are approximately 100,000 distinct Key Numbers).; A topic’s classification and relevant Key Numbers may be determined by consulting the digest’s Descriptive-Word Index.

Once the appropriate topic and Key Number are identified, cases on that subject may be located using that Key Number in the federal digest or any regional or state digest.

Additionally, if the name of a case and the court in which that case was decided are known, a citation may be identified in the Table of Cases volume of the appropriate digest. Supplementary pocket parts (placed in the back of bound volumes) or separate interim pamphlets are used to update the digests.

Note: LexisNexis is another major U.S. legal publisher and it uses its own system of Headnotes and Summaries, although it does not publish a digest system like West does.