California Defamation (Libel and Slander) Statutes    

The following sections are taken from the California Civil Code:

45. Libel is a false and unprivileged publication by writing, printing, picture, effigy, or other fixed representation to the eye, which exposes any person to hatred, contempt, ridicule, or obloquy, or which causes him to be shunned or avoided, or which has a tendency to injure him in his occupation.

45a. A libel which is defamatory of the plaintiff without the necessity of explanatory matter, such as an inducement, innuendo or other extrinsic fact, is said to be a libel on its face. Defamatory language not libelous on its face is not actionable unless the plaintiff alleges and proves that he has suffered special damage as a proximate result thereof. Special damage is defined in Section 48a of this code.

46. Slander is a false and unprivileged publication, orally uttered, and also communications by radio or any mechanical or other means which: 1. Charges any person with crime, or with having been indicted, convicted, or punished for crime; 2. Imputes in him the present existence of an infectious, contagious, or loathsome disease; 3. Tends directly to injure him in respect to his office, profession, trade or business, either by imputing to him general disqualification in those respects which the office or other occupation peculiarly requires, or by imputing something with reference to his office, profession, trade, or business that has a natural tendency to lessen its profits; 4. Imputes to him impotence or a want of chastity; or 5. Which, by natural consequence, causes actual damage.

47. A privileged publication or broadcast is one made:

(a) In the proper discharge of an official duty.

(b) In any (1) legislative proceeding, (2) judicial proceeding, (3) in any other official proceeding authorized by law, or (4) in the initiation or course of any other proceeding authorized by law and reviewable pursuant to Chapter 2 (commencing with Section 1084) of Title 1 of Part 3 of the Code of Civil Procedure, except as follows:

    (1) An allegation or averment contained in any pleading or affidavit filed in an action for marital dissolution or legal separation made of or concerning a person by or against whom no affirmative relief is prayed in the action shall not be a privileged publication or broadcast as to the person making the allegation or averment within the meaning of this section unless the pleading is verified or affidavit sworn to, and is made without malice, by one having reasonable and probable cause for believing the truth of the allegation or averment and unless the allegation or averment is material and relevant to the issues in the action.

    (2) This subdivision does not make privileged any communication made in furtherance of an act of intentional destruction or alteration of physical evidence undertaken for the purpose of depriving a party to litigation of the use of that evidence, whether or not the content of the communication is the subject of a subsequent publication or broadcast which is privileged pursuant to this section. As used in this paragraph, "physical evidence" means evidence specified in Section 250 of the Evidence Code or evidence that is property of any type specified in Chapter 14 (commencing with Section 2031.010) of Title 4 of Part 4 of the Code of Civil Procedure.

    (3) This subdivision does not make privileged any communication made in a judicial proceeding knowingly concealing the existence of an insurance policy or policies.

    (4) A recorded lis pendens is not a privileged publication unless it identifies an action previously filed with a court of competent jurisdiction which affects the title or right of possession of real property, as authorized or required by law.

(c) In a communication, without malice, to a person interested therein, (1) by one who is also interested, or (2) by one who stands in such a relation to the person interested as to afford a reasonable ground for supposing the motive for the communication to be innocent, or (3) who is requested by the person interested to give the information. This subdivision applies to and includes a communication concerning the job performance or qualifications of an applicant for employment, based upon credible evidence, made without malice, by a current or former employer of the applicant to, and upon request of, one whom the employer reasonably believes is a prospective employer of the applicant. This subdivision authorizes a current or former employer, or the employer's agent, to answer whether or not the employer would rehire a current or former employee. This subdivision shall not apply to a communication concerning the speech or activities of an applicant for employment if the speech or activities are constitutionally protected, or otherwise protected by Section 527.3 of the Code of Civil Procedure or any other provision of law.

(d) (1) By a fair and true report in, or a communication to, a public journal, of (A) a judicial, (B) legislative, or (C) other public official proceeding, or (D) of anything said in the course thereof, or (E) of a verified charge or complaint made by any person to a public official, upon which complaint a warrant has been issued. (2) Nothing in paragraph (1) shall make privileged any communication to a public journal that does any of the following: (A) Violates Rule 5-120 of the State Bar Rules of Professional Conduct. (B) Breaches a court order. (C) Violates any requirement of confidentiality imposed by law.

(e) By a fair and true report of (1) the proceedings of a public meeting, if the meeting was lawfully convened for a lawful purpose and open to the public, or (2) the publication of the matter complained of was for the public benefit.

Some words of explanation:

Section 45 refers to what is called "libel on its face."  If you publish on your website that "Joe Dokes is a liar," that statement is libelous on its face (if it is false), because the reader does not need any other facts to understand the defamatory statement.  On the other hand, if you wrote, "That guy that is constantly posting messages about me is a liar," still referring to Joe Dokes, the reader needs additional information to determine who you are talking about.  You may still be guilty of defamation, but the law makes the burden higher, and Joe Dokes would need to allege and prove special damages.

What are special damages?  That term is defined in Section 48a, which also specifies some procedural steps that must be taken when the defamation is by a newspaper or radio broadcast:

48a.

1. In any action for damages for the publication of a libel in a newspaper, or of a slander by radio broadcast, plaintiff shall recover no more than special damages unless a correction be demanded and be not published or broadcast, as hereinafter provided. Plaintiff shall serve upon the publisher, at the place of publication or broadcaster at the place of broadcast, a written notice specifying the statements claimed to be libelous and demanding that the same be corrected. Said notice and demand must be served within 20 days after knowledge of the publication or broadcast of the statements claimed to be libelous.

2. If a correction be demanded within said period and be not published or broadcast in substantially as conspicuous a manner in said newspaper or on said broadcasting station as were the statements claimed to be libelous, in a regular issue thereof published or broadcast within three weeks after such service, plaintiff, if he pleads and proves such notice, demand and failure to correct, and if his cause of action be maintained, may recover general, special and exemplary damages; provided that no exemplary damages may be recovered unless the plaintiff shall prove that defendant made the publication or broadcast with actual malice and then only in the discretion of the court or jury, and actual malice shall not be inferred or presumed from the publication or broadcast.

3. A correction published or broadcast in substantially as conspicuous a manner in said newspaper or on said broadcasting station as the statements claimed in the complaint to be libelous, prior to receipt of a demand therefor, shall be of the same force and effect as though such correction had been published or broadcast within three weeks after a demand therefor.

4. As used herein, the terms "general damages," "special damages," "exemplary damages" and "actual malice," are defined as follows: (a) "General damages" are damages for loss of reputation, shame, mortification and hurt feelings; (b) "Special damages" are all damages which plaintiff alleges and proves that he has suffered in respect to his property, business, trade, profession or occupation, including such amounts of money as the plaintiff alleges and proves he has expended as a result of the alleged libel, and no other; (c) "Exemplary damages" are damages which may in the discretion of the court or jury be recovered in addition to general and special damages for the sake of example and by way of punishing a defendant who has made the publication or broadcast with actual malice; (d) "Actual malice" is that state of mind arising from hatred or ill will toward the plaintiff; provided, however, that such a state of mind occasioned by a good faith belief on the part of the defendant in the truth of the libelous publication or broadcast at the time it is published or broadcast shall not constitute actual malice.

If you want to learn more, here is an article summarizing these California statutes.