Defamation of character occurs when a person makes a published false, and harmful statement about someone. Defamation takes two forms, slander (oral defamation) and libel (written defamation).
There are a number of important defenses in a defamation lawsuit that could either eliminate the plaintiff's claim entirely or weaken it significantly.
First and foremost, truth is an absolute defense to a defamation lawsuit. If the statement that is the subject of the suit is true, and you can prove it, your attorney can move to have the plaintiff's claim dismissed. No one is punished for speaking the truth, even if it is an ugly truth.
Absolute privilege is also a complete defense to a lawsuit. Some types of statements -- or the settings in which they are made -- are privileged no matter how negative they may be. For example, arguments that lawyers make in court, comments judges make, and testimony given by witnesses in a trial are all absolutely privileged. There is a strong interest in promoting vigorous advocacy from attorneys and truthful testimony from witnesses, so people cannot be punished for things they say in those contexts. Also, the fact that witnesses testify under oath lends credence to what they are saying, and that testimony is always protected.
See The "Privilege" Defense in a Defamation Case for detail on this important legal concept.
Even if you are not sure whether the above defenses would apply to you, there are other defenses your attorney may be able to raise to ultimately have the case dismissed without a trial, or to at least reduce the amount of damages the plaintiff recovers.
Qualified privilege is another common defense to a defamation action. Sometimes, even if a statement is not absolutely privileged, the context in which it was made means that it should be privileged anyway. An example might be statements a reporter makes about a matter of public interest in the community. Even if the information puts a person in a negative light, some subjects are so important to the public in general that they will be protected.
Another defense you may be able to raise is that you were speaking an opinion, not a fact. Defamation claims must involve false statements of fact -- that is, statements that are made as if they are fact and not merely opinion.
The difference would be something like this: If a person says, "The judge took a bribe," that is presented as if it were fact, and it would be actionable if it is false. But, if a person says "I think that judge is crooked," that seems more like an opinion and it might not be actionable because opinions generally are protected speech under the law.
Another example of opinion may be a political cartoon. While the artist may be speaking about some factual situation, the presentation of the material is almost always an opinion because most people know that is the nature of political cartoons.
Whether your statement is considered opinion or not is largely dependent upon the context in which you made it. You will need to ask yourself whether a person hearing or reading the statement would think it was a fact based on your presentation of it, or based on how well you know the subject or person about which you are speaking or writing.
Similar to opinion is the defense of "fair comment on a matter of public interest." If, for example, someone makes a statement about the actions of people on a school board, the statement might be protected because there likely is a strong public interest in the activities of the school board. These types of statements tend to involve local politics or community activity. Similar to the opinion defense, whether this defense is available to you depends on the subject matter and the context in which it was made.
Innocent dissemination is slightly less common, but still may be a viable defense. For example, a newsletter printer or publisher may raise this defense if the newsletter contains a defamatory statement. The writer of the material in the newsletter made the statement, and the publisher or printer may or may not have read the material. Therefore, they may not be responsible for the contents of the newsletter.
Lastly, a common defense is that the plaintiff already had a poor reputation. While this does not necessarily mean the suit will be dismissed in its entirety, it can reduce the credibility of the plaintiff's claims and affect a jury's decision if evidence of the plaintiff's reputation comes in at trial. It could also make the plaintiff more likely to settle and/or reduce his or her recovery.