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U.S. Legal Research: Case Law

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U.S. Legal Research: Complete Guide (PDF)




I. Introduction to Primary Legal Sources
II. Case Law Research: Background Information
III. Structure of a Case in a West Case Law Reporter
IV. How to Find a Case by Subject
V. Constitutional Legal Research
VI. Updating Case Law (Shepard's and KeyCite)

I. Introduction to Primary Legal Sources

In legal research vocabulary, the term “primary sources” refers to sources of the law itself.  In other words, primary sources of law are the texts of enactments by governments containing rules that govern a jurisdiction.  In sum, secondary sources of law (discussed above) are works about the law; primary sources are the law itself.

There are two different general designations for primary sources of law: official and unofficial.  Official primary sources of law are texts that are published and/or printed by the enacting government.  Unofficial primary sources of law are texts of law published by private publishers (often, but not exclusively, West or Lexis Publishing). 

In some jurisdictions, there is no official publication of certain resources and only the unnofficial version exists.  For example, federal case law at the appellate and trial level is only published by West.  In law practice, attorneys are usually required to cite to an official source, where one exists.  However, for legal research, always use the unofficial source because the private publishers will add value to the text of the primary law by including tools and materials that will aid in the legal research process

Each branch of government, both at the federal and state level, produces law.  Understanding the overall landscape of the legal sources is helpful before beginning research of one source or one area of law. The chart below is a simplified overview of the universe of federal law, listing the major types of law publications of each branch.  Most state governments will produce law in a similar set-up.



The Constitution
↓ ↓ ↓



Branch of Govt.





Type of Law Produced

Case Law




Chronological Publication of Law

Case Law Reporters

Session Laws (Stat. at Large)

 The Federal Register


Publication of Law By Subject


United States Code (USC)

Code of Federal Regulations (CFR)


Note that each government branch produces law that is published chronologically.  The public laws and regulations are then published in codes by subject.  Case law is not published by subject (thus, research case law requires a “finding tool” to locate cases by subject).  The following sections will discuss research of each type of primary law in detail.

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II. Case Law Research: Background Information

Courts in the U.S. legal system resolve disputes presented to them by parties.  Courts issue written opinions explaining the court’s resolution of the dispute and its underlying reasoning.  If the opinion is published, it will be found in a case reporter.


A. Binding Authority and Precedent

Why would a legal researcher care what a judge decided in some legal dispute between two private parties?  Central to the U.S. legal system is the idea of binding authority and precedent

When a higher court publishes a decision on a point of law, that decision is binding on all lower courts in the same jurisdiction.  The lower courts in that jurisdiction must follow earlier judicial decisions when the same points of law arise again in litigation.  A court opinion that has this power has binding authority or precedent. This concept is formally called stare decisis (Latin – “to stand by things decided”).

Because this power extends only to lower courts in same jurisdiction as the higher court, often legal research will require a basic understanding of jurisdiction and court system structures.  The federal court system and most state court systems maintain a three-tiered structure.  The table below illustrates this typical structure in the federal system, New Jersey and New York.


B. Court System Structure*

Typical Court
System Structure

State Courts (vary by state)
(New Jersey)
(New York)


Federal Courts

High Court

State Supreme Court
(Supreme Court of NJ)
(NY Court of Appeals)

United States Supreme Court


Appellate Court

State Appellate Court(s)
(Appellate Division)
(Appellate Division)

United States Circuit Courts of Appeals


Trial court

State Trial Courts
(Superior Court of NJ)
(Supreme Court of NY)

United States District Courts

*Note that in NY, the trial court (the lowest court) is called the “Supreme Court.”  Also many jurisdictions maintain several types of trial level courts in addition to the main trial court.  These can include family courts, traffic courts, criminal courts, municipal courts, county courts and many others.

The U.S. Supreme Court’s opinions are binding on all courts in the U.S. In the federal system, the country is divided up into 13 circuits, each having a Circuit Court of Appeals, whose opinions are binding on all trial courts (District Courts) in that Circuit.  New Jersey is part of the Third Circuit.  The Third Circuit Court of Appeals sits in Philadelphia.  New York is part of the Second Circuit and its Court of Appeals sits in New York City.  A map of all the circuits is posted at

Each state has its own system for carving up the state and assigning jurisdictions.  If your research requires knowledge of these jurisdictional divisions, many states post this information on the state court system’s web site.  Another helpful resources is the National Center for State Court’s web site:


C. Case Law Reporters

Court opinions are published more or less chronologically in case law reporters.  Cases from different jurisdictions are published in different reporters.  Some courts, but not nearly all, still publish official reporters. The major publisher of unofficial case law reporters is West.  When possible, it’s helpful to use the West reporters when researching case law in print.  West has designed an indexing system that makes finding cases by subject rather easy.  This will be discussed in the section below on digests. 

The table below outlines the federal case law reporters.  Only the Supreme Court maintains an official reporter.




U.S. Supreme Court

United States Reports (official)
Supreme Court Reporter (West)
Lawyers’ Edition  (Lexis)

S. Ct.
L. Ed.

Federal Circuit Courts of Appeal

Federal Reporter (West)
Federal Reporter 2nd Series
Federal Reporter 3rd Series

F. 3d

Federal District Courts

Federal Supplement (West)
Federal Supplement 2nd Series

F. Supp.
F. Supp.2d

All of these federal case law reporters, except the Supreme Court Reporter, are located  at law collection in the Social Science Reference Center (Law Cases and Statutes (LAW)).  The Supreme Court Reporter is located in the stacks at Firestone Library at KF101 .A322 Vols. 1 – 112 (1882 – 1991) only.

For state case law, the West Regional Reporters publish opinions from the high courts and some intermediate appellate court of the 50 states.  The table below lists all the states and the regional reporter where the case law from that state is printed.





Atlantic Reporter
Atlantic Reporter 2nd Series



Northeastern Reporter
Northeastern Reporter 2nd Series



Northwestern Reporter
Northwestern Reporter 2nd Series



Pacific Reporter
Pacific Reporter 2nd Series
Pacific Reporter 3rd Series



Southeastern Reporter
Southeastern Reporter 2nd Series



Southwestern Reporter
Southwestern Reporter 2nd Series



Southern Reporter
Southern Reporter 2nd Series



New York Supplement
New York Supplement 2nd Series



California Reporter
California Reporter 2nd Series
California Reporter 3rd Series

Cal. Rptr.
Cal. Rptr.2d
Cal. Rptr.3d

Princeton University Library only holds the Atlantic Reporter in full in print.  It is located in the hallway outside the Social Science Reference Center (Law Cases and Statutes (LAW)).  A partial set of the Northeastern Reporter is located in the stacks at Firestone Library KF135.N6 N63.

All of the regional reporters are full-text searchable on Westlaw Campus, Lexis Academic, Westlaw Commercial, and Lexis Commercial.  However, only the West products allow access to West’s digest system for finding cases by subject.  For more information, see the sections below on digests and Westlaw.


D. Case Citations

A case is easily retrievable by citation, both in print and in the electronic databases.  The structure of a case citation is “volume# / reporter abbreviation / first page of case”:


Reporter Abbreviation

First Page of Case




Sample Citations:
U.S. Supreme Court (official):      120 U.S. 354
U.S. Supreme Court (West):       189 S. Ct. 698
Federal Reporter:                       1 F.3d 67
Federal Supplement:                  33 F.Supp.2d 87
Atlantic Reporter:                       608 A.2d 1341  

A full case citation includes the case name, all reporters where the case appears, court information (except for the U.S. Supreme Court) and year:

Brown v. Board. of Ed., 347 U.S. 483, 74 S.Ct. 686, 98 L.Ed. 873 (1954).
National Abortion Federation v. Gonzales, 437 F.3d 278 (2d Cir. 2006).
Hollenbaugh v. Carnegie Free Library, 436 F.Supp.1328 (W.D. Pa. 1977).
Hummel v. Reiss, 608 A.2d 1341, 129 N.J. 118 (N.J. 1992).

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West is the major private print publisher of case law reporters.  In addition to the text of the court opinions, West includes several features that help the researcher quickly understand the case and find cases on a similar topic.  The following research features appear in West case law reporters, after the court name, case parties, docket number, and date, but before the actual court opinion begins:

West Summary: a small paragraph briefly summarizing the entire case.  This paragraph is written by editors at West Publishing, not the court, and therefore may not be cited as law.

Opinions Included: a listing of the of the court opinions, any concurring dissenting opinions, the authors or each opinion, and if applicable, who joined in each opinion.

West Headnotes and Key Numbers: one or more small paragraphs with a heading (consisting of a number, topical heading, and an icon that looks like a key with another number).  These paragraphs summarize the each legal point and is assigned a “Topic” and a “Key Number” that represents a subtopic.  The number at the left of the heading is the number of the headnote and will correspond to a number in the text of the court opinion where the court makes the legal point summarized in the headnote.  In the example headnote below, the headnote is headnote 1.  A number 1 will appear in the text of the court opinion where the legal point summarized in the headnote is made.  The Topic is Negligence and the Key Number is 210.  The headnotes are a good way to quickly learn what legal rulings the court made before reading the text of the case (which can sometimes be difficult to read).  The topic and key number are used to find other cases that address that same topic.  This is addressed in the section below on digests.

[1] Negligence key210
272k210 Most Cited Cases
(Formerly 272k2)
In every instance before negligence can be predicated of a given act, back of the act must be sought and found a duty to the individual complaining, the observance of which would have averted or avoided the injury.

Court Syllabus:  a summary of the court’s opinion, written by the court, but not part of the actual decision.  Most opinions do not have a syllabus.  Usually it is only U.S. Supreme Court decisions.  The court’s syllabus is longer than the West summary.  This syllabus may not be cited as law.    

Attorneys: following the syllabus (or, in the absence of a syllabus, following the headnotes) is a listing of the attorneys involved in the court case.

The Opinion: only after the listing of the attorneys does the court’s opinion begin.
For an examples of West court opinions, with each of these features labeled, see the Palsgraf case (PDF) and the Gratz case (PDF).

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If you do not have a case citation, and you need to find cases on a particular subject, you need to use some sort of “finding tool” because the cases in the reporters are published in (more or less) chronological order.

A. Digests

Digests are the major tools to find cases by subject, both in print and on Westlaw.  Each set of West-published case law reporters has a companion set of digests.  The Decennial Digests covers cases across jurisdictions for a ten-year period.

The digests are organized by subject according to West’s Topics and Key Numbers.  By looking up the West Topic and Key Number that represents your research subject, you’ll find a listing of every case in that case law reporter series that has been assigned your Topic and Key Number.  Along with the case name will be a reprint of the headnote that is found along with the court’s opinion in the case law reporter.

The first step in using the digests is to find a relevant Topic and Key Number.  To find a Topic and Key Number, use the “Descriptive Word Index” at the end of the digest set.  In the alternative, if you have already located a relevant case (either from a secondary resource or from a full-text search), browse its headnotes for the Topic and Key Number that best suits your research subject.   Finally look up the relevant Topic and Key Number in the digests. The same Topic and Key Number may be used in any digest for any jurisdiction. 

The digest system is also accessible on Westlaw, where it is called KeySearch.  Using the Topics and Key Numbers on Westlaw is quite simple and is often more effective than full-text searching alone.

Below is a listing of digests held by Princeton University Library:

Federal Digest
Firestone Library (F)
Covers cases through 1939

Modern Federal Practice Digest
Firestone Library (F)
Covers cases from 1940 through 1960

West’s Federal Practice Digest (2d – 4th)
Firestone Library, Social Science Reference Center (LAW)KF127 .W481961-present

West's Atlantic Digest 2d.
Firestone Library, Social Science Reference Center (LAW) 
Covers cases from 1940 to the present.

American Digest, Century Edition
Firestone Library, Social Science Reference Center (LAW) 
Abstracts of state court cases from 1658 to 1896.

American Decennial Digest
Firestone Library, Social Science Reference Center (LAW) 
Decennial Edition, 1897 –1906                            7683.922.3
Second Decennial Edition, 1907 – 1916               7683.922.31
Third Decennial Digest, 1916 – 1926       7683.922.32
Fourth Decennial Digest, 1926 – 1936     7683.922.321
Fifth Decennial Digest, 1936 – 1946        7683.922.323
Sixth Decennial Digest, 1946 – 1956                   7683.922.324
Seventh Decennial Digest, 1956 – 1966              7683.922.325
Eighth Decennial Digest, 1966 – 1976     7683.922.328
Ninth Decennial Digest, Part I, 1976 – 1981          KF141 1976
Ninth Decennial Digest, Part II, 1981 – 1986         KF141 1981
Tenth Decennial Digest, Part I, 1986 – 1991         KF141 1986
Tenth Decennial Digest, Part II, 1991 – 1996        KF141 1991
Eleventh Decennial Digest, Part I, 1996 – 2001     KF141 2000
West’s General Digest, Supplement                   KF141 Suppl.

B. Full-Text Searching

Full-text searching, while a powerful and important method to locate cases by subject, should not be the only research method used.  Full-text searching is most effective when used in combination with the digests and the other methods discussed in this section.  This is especially true for less-experienced legal researchers who have not been though law school and may be unfamiliar with legal language, legal reasoning and the typical structure of a court opinion.  That stated, however, full-text searching on Westlaw and Lexis is a powerful way to find cases.

At Princeton, the primary way to conduct full-text case law research is on Westlaw Campus or Lexis Academic.  Both databases are available on the Library’s web page by following the “Articles & Databases” Link, choosing “Law” and then choosing “United States Law.”

To find cases by subject in both Westlaw Campus and Lexis Academic first choose which type of case law you would like to search, federal or state. (Westlaw Campus will default to a legal research page, while on Lexis Academic you must follow the legal research link on the left).  Then conduct either a “Terms & Connectors” search (similar to a Boolean search) or a “Natural Language” (keyword) search.

When viewing cases on Westlaw Campus, you’ll see the same research features you’ll find in the West case law reporters, including the headnotes, Topics and Key Numbers.  There is also electronic access to the entire digest system, either by clicking on the Topic and Key Number in a case’s headnotes or by conducting a KeySearch.

Lexis cases also have research features such as a summary of the case and headnotes.  However the Lexis headnotes are not the same headnotes found in the print case law reporters. 

C. Secondary Sources

Secondary sources are an important way to begin research to learn about an area of law.  They are also excellent ways to find cases by subject.  Secondary resources will always include citations to case law of the subject area it is covering.  

Once you have found a secondary resource on your subject, simply pull the cases in the citation.  This is a great strategy for getting started on case law research.

It is helpful to think of secondary resources as legal research that is already completed.  It does not make sense to start from scratch when someone else has already conducted the research and collected the case law on your topic.

D. Statutes Annotated

While statutory research is discussed in detail below, the Statutes Annotated is also an effective case law research tool if you are looking for cases that apply a particular statute. 

The Statutes Annotated are privately published (usually by West) statutes.  They print the text of the statutes.  After the text of each statute, the editors include annotations that provide detailed information about each statute.  One of these annotations is called “Notes of Decisions,” which lists short summaries of all the cases that have addressed or applied that statute.

If you are seeking cases related to a statute or your issue is related to a statute, find that statute in the Statutes Annotated (using the index) and then check the Notes of Decision for relevant cases.  See the section on statutes below for more information on statutory research.

E. Shepard’s/KeyCite

Checking the citing references of a case on Shepard’s or KeyCite will provide citations to cases on the same subject.  For more information see the section on Shepard’s/KeyCite below.

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V. Constitutional Research

A large part of constitutional research is actually case law research because it is the courts that decide whether a law is constitutional. However, secondary resources are especially important in constitutional research as well. Because issues of constitutional law are especially suited to complex analysis that is common in law reviews, law journals and monographs, these resources are especially helpful and important in constitutional research.  

A. U.S. Code Annotated as a Constitutional Research Tool

Also, although the constitution is not a statute, the text of the constitution is printed in the first volumes of the U.S. Code Annotated.  Each section of the constitution is annotated with citations to related secondary resources and, most importantly, citations to case law related to and applying that section.  The U.S. Code Annotated is an extremely important constitutional research tool.

United States Code Annotated (U.S.C.A.) – published by West
Firestone Library, Social Science Reference Center (LAW)

B. Analysis and Commentary

Constitutional Law, 6th edition / Nowak & Rotunda
Firestone Library, Social Science Reference Center 
KF4550 .N6 2000

Treatise on Constitutional Law, 3rd edition  / Nowak & Rotunda
Firestone Library, Social Science Reference Center 
KF4550 .R63 1999
This multi-volume treatise is more detailed than the single volume treatise above and is updated by annual pocket parts.

American Constitutional Law, 3rd edition / Laurence H. Tribe
Firestone Library, Social Science Reference Center 
KF4550 .T785 2000

Constitutional Law in a Nutshell, 5th edition / Barron & Dienes
Firestone Library, Social Science Reference Center 
KF4550.Z9 B35 2003

In sum, the U.S. Code Annotated, case law (and all the resources used to find case law, such as digests), law review articles, treatises and monographs (found through catalog searching) are the major resources for constitutional research.

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 VI. Updating Case Law (Shepard's and KeyCite)

Cases are frequently reversed or overturned.  Therefore, if you want to verify that a case’s ruling is still good law you must use a citator.  There are two different case law citators: Shepard’s (published in print and online by Lexis) and KeyCite (published only online, by West).  The process of updating case law is often called “shepardizing” or “keyciting.” Using the print Shepard’s can be very difficult and time consuming.  It is recommended to only use online Shepard’s or KeyCite.

Shepard’s and KeyCite are powerful research tools that tell the researcher much more than whether a case is still good law.  Shepard’s and KeyCite are “windows into the future” of a case.  In other words, when you shepardize or keycite a case, you will learn happened to that case and to the legal rule from that case, after it was decided. 

When learning how to shepardize and keycite, it’s helpful to think of the following scenario:  you’ve found a case and before using it you want to find out information about that case that is not available just from reading it. The three major types of information Shepard’s and KeyCite provides about “your case” are:

Citing references are designated according to how they treat the case you are shepardizing/keyciting (“your case”) as positive (meaning citing reference agrees with “your case”) or negative (the citing reference disagrees with “your case”).  KeyCite breaks down the negative treatment into more subcategories, such as “Called into Doubt” or “Declined to Extend” or “Distinguished.”

How to Use Shepard’s / KeyCite

Shepard’s (online) and KeyCite are quite simple to use.  First, pull up the case you are interested in shepardizing/keyciting. You can do this by entering the citation or by doing a full-text or digest search.

Once you have the case on the screen:

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