When judges and courts decide cases, they often write opinions in which they explain their reasoning in reaching their decisions. These judicial opinions are an important source of legal authority in the United States. Courts try to decide cases on the basis of principles and rules established in earlier cases (called precedents). Some opinions are stronger precedents than others. The precedential value of an opinion depends largely on the level and jurisdiction of the court that decided the case.
In the federal judicial system, the decisions of the highest court, the United States Supreme Court, have high precedential value and are binding on all federal courts. In contrast, the decisions of the trial level federal courts (called District Courts) are not binding on any courts, even though they are often cited as persuasive authority. Between these two levels are the 13 U.S. Courts of Appeals, most of which have jurisdiction over a particular geographic area or "circuit." California is included in the Ninth Circuit. A case decided by a particular Circuit Court of Appeals is binding only on the District Courts within that circuit.
Many, though not all, judicial opinions are published in case reporters. Each jurisdiction has at least one case reporter. In order to find a case in a case reporter, you will need to have the case "citation," which tells you which reporter volume and page to consult.
The following is an example of a citation to a United States Supreme Court case:
According to this citation, the case begins on page 238 of volume 464 of the United States Reports (abbreviated as U.S.). Additional examples of case citations, as well as a list of the major court reporters in the United States (along with their standard abbreviations), can be found in the USC Law Library's Guide to Legal Abbreviations and Citations.