Defamation is any intentionally false communication, written or spoken, that exposes a person to hatred, contempt, ridicule, causes him to be shunned or avoided, or has a tendency to injure him in his occupation.  Defamation when written is called libel, and when spoken is called slander.

There are two types of defamation: defamation and defamation per se.  A person bringing a claim for defamation generally must prove damages.  That means that the plaintiff must set out the actual injuries he suffered, explain that the defamation caused the injuries, and clearly show the cost of those injuries.  A person bringing a claim for defamation per se need not prove damages because the law "presumes" damages.  Defamation per se occurs when the defamation imputes to the person claiming injury:

1. Criminal activitiy, indictment, or conviction of a crime
2. Infectious, contagious or "loathsome" diseases
3. Tends to directly injure the person in his office, profession, trade or business by imputing to him disqualification, incompetence, or something that has a natural tendency to lessen his profits
4. Impotence, or a "want of chastity"

The California defamation rules are very clearly discussed at Sections 44-48.8 of the California Code of Civil Procedure.

Police may sue for defamation for false complaints alleging misconduct, criminal conduct, or incompetence if the complaint is false, made with knowledge that it was false and was made with spite, hatred, or ill will.  The officer may prove the complaint was false by showing that the person who made the complaint had no reasonable ground to believe it was true and also exhibited a reckless disregard for learning the truth.  CCP 47.5.

Statements made in the course of litigation by judges, parties, witnesses, and their attorneys are generally exempt from defamation claims under the "litigation privilege."

Most defamation suits place the burden on the defaming party, usually the defendant, to prove that the defamatory statements were true.  Truth is an absolute defense to defamation.

There are also important exceptions for public figures, who must prove "actual malice" by "clear and convincing" to win a claim for defamation.  Actual malice means that the statements were made with knowledge or reckless disregard that they were false.  New York Times v. Sullivan, 376 U.S. 254 (1964).

Before Sullivan, Southern states were using libel laws to intimidate newspapers that were reporting on the civil rights movement.  At that time there were almost $300 million in libel actions outstanding against news media in the South.  After Sullivan, newspapers were freer to report developments in the civil rights movement.  In Sullivan, the New York Times carried a full paid advertisment seeking donations to defend Martin Luther King, Jr. against a perjury indictment (see copy of ad here).

The advertisement criticized police officials in Montgomery, Alabama and L. B. Sullivan, the Montgomery Public Safety Commissioner sued, although he was not personally named in the advertisement.  The Supreme Court ruled 9-0 that the actual malice standard was appropriate in defamation cases regarding public figures because the First Amendment protects open and robust debat on public issues that often includes

vehement, caustic, unpleasantly sharp attacks on government and public officials.

Figuring out who is a public and who is a private figure for defamation law purposes can be difficult.  For a person to be a public figure in all situations, the person's name must be so familiar as to be a household word.  Because many public figures are not so well known, courts adopted the "limited-purpose public figure" doctrine where a person who is voluntarily injected into a public controversy becomes a public figure for a limited range of issues relating to the controversy.

Courts have reasoned that limited-purpose public figures have at least temporary access to means to counteract false statements about them and they voluntarily place themselves in the public eye and so voluntarily relinquish some of their privacy rights.  False statements about limited-purpose public figures that relate to the public controversies in which those figures are involved are not considered defamatory unless they meet Sullivan's actual malice test.  Key in determining whether a person is a limited-purpose public figure is whether they voluntary injected themselves into a matter of public controversy, generally in an effort to influence others on that matter of public controversy.