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Case Law Research: Using Secondary Sources

This guide provides information on Case Law Research, and identifies pertinent print and online resources available through the NYU Law Library


If you do not have a specific citation you are searching for, the best place to start your research is with secondary sources. Secondary sources are materials that discuss, explain, analyze, and critique the law. They discuss the law, but are not the law itself. Secondary sources, such as Encyclopedias, American Law Reports, and Treatises are a great place to start your legal research.  Unlike primary materials (case law, statutes, regulations), secondary sources will help you learn about an area of law, and provide you with citations to relevant primary materials, including cases.


Encyclopedias: A legal encyclopedia publishes a comprehensive collection of brief articles on legal topics. They are a great place to start your research on a new topic since they offer a general introduction to a legal topic, and often include citations to cases. The two main legal encylopedias are American Jurisprudence (Am. Jur., Am. Jur.2d) and Corpus Juris Secondum (C.J.S.). 

American Law Reports

American Law Reports: A.L.R., is available in print and on Westlaw and Lexis.  A.L.R. used to contain references to both federal and state cases, but as of the 4th series, the federal cases have been moved to A.L.R. Federal (the A.L.R. has been published in eight series - A.L.R. - A.L.R. 6th and A.L.R. Federal and A.L.R. Federal 2d).  It is a compilation of attorney written annotations (articles) that analyze a particular legal issue.  These tend to be more indepth than an encylopedia article, and provide citations to cases on both sides of the issue.  You can search for annotations on your topic using the Index volumes at the end of the set of series volumes.  Once you have found an annotation on your topic, use the citation given to look up the annotation in the set.  For example, if you were interested in finding cases relating to the Class Action Fairness Act, you could go to the A.L.R. Federal 2d Quick Index and look up class actions.  Under Class Action Fairness Act, you would find a citation to "18 A.L.R. Fed. 2d 223."  Once you have the citation, you can go to the volume, in this case volume 18, page 223.  Make sure that you are looking in the correct series, in this case A.L.R. Fed. 2d. Annotations contain short descriptions of cases relating to the legal issue discussed, along with a citation to the case.  You may then find that case by citation using one of the federal reporters.

Treatises, Hornbooks, and Nutshells

Legal treatises and hornbooks are law books that provide an in-depth treatment of an area of law - generally written by a practitioner or scholar with a specialization in that area of law.  The Nutshell series of books also focus on a particular subject area, but are generally written in a more user-friendly, less scholarly manner.   These books provide a useful starting point for finding case law on a particular subject in a more scholarly context.  Unlike encyclopedia articles, legal treatises tend to go into greater depth and provide a more analytical approach to the subject.


While case law reporters are generally organized chronologically, Digests are multi-volume indexes to the law organized by topic and "key number" classification system.  The topics are broad areas of law, with the "key numbers" providing a more narrow subtopic.

To use the digests, first try to select key words associated with your topic, or that describe your topic. West's Federal Digest includes a "Descriptive-Word Index" to find authorities using words that describe the legal concept you are interested in. The West Index will provide the West Topic and Key Number associated with your keywords.  It will give you the volume number of the digest addressing your topic.  Cases are listed in reverse chronological order, from the final appellate court down to reported trial court opinions.  Note the citations of cases you find that appear to be relevant to your search.

In addition to West's Federal Digests, and West's General Digests which contain both Federal and State materials, many states have individual digests which cover state and federal cases for that particular state.  West's NY Digests are in MRR and B2.  The library also keeps up-to-date digests for the following key jurisdictions: California, Florida, Illinois, Maryland, Massachusetts, Michigan, New Jersey, Ohio and Texas.  These are located in the Golieb Room.

Westlaw (password required): Access to West's Digest system is available through Westlaw.  There are several ways to search the Digest system - through Key Number Search, Browsing the Digest (an alphabetical listing of over 400 legal topics), Searching for Specific Topic and Key Number (if you already know the relevant numbers), and KeySearch.  You can also create custom digests - you can access custom digests by going to "Key Numbers & Digests" from the "More" dropdown list on the toolbar.  To create a custom digest, look for topic and key numbers that are relevant to your research and Custom Digest will retreive the relevant headnotes.  If you do not know how to use the digest system, KeySearch helps you create a search by identifying the relevant terms and key numbers to your legal issue and creates a query for you.

Lexis (password required): Lexis uses a Headnote system to categorize and classify cases, but does not assign numbers to the various legal topics and sub-topics. Lexis provides two main ways to search by topic - you can search for a topic with a key word or phrase, or you can browse the alphabetical list of topics.  When browsing subject alphabetically, clicking on the topic will provide more narrow subjects within that topic.  You may then conduct a search within that topic, utilizing the options to restrict or refine your search.  Once you have found a case, you can use the Headnote at the top to find other relevant cases.  Each headnote also has a "More Like This Headnote" link that will take you to a search screen with options to refine or restrict the search.