Defamation—also calumny, vilification, and traducement—is the communication of a false statement that harms the reputation of an individual person, business, product, group, government, religion, or nation as well as other various kinds of defamation that retaliate against groundless criticism.

Under common law, to constitute defamation, a claim must generally be false and have been made to someone other than the person defamed. Some common law jurisdictions also distinguish between spoken defamation, called slander, and defamation in other media such as printed words or images, called libel.

False light laws protect against statements which are not technically false but misleading.

In some civil law jurisdictions, defamation is treated as a crime rather than a civil wrong. The United Nations Commission on Human Rights ruled in 2012 that the criminalization of libel violates freedom of expression and is inconsistent with Article 19 of the International Covenant on Civil and Political Rights.

A person who defames another may be called a "defamer", "famacide", "libeler" or "slanderer".