Negative campaigning is the process of deliberately spreading negative information about someone or something to damage their public image. A colloquial and more derogatory term for the practice is mudslinging.

Deliberate spreading of such information may be motivated either by a genuine desire to warn others against real dangers or deficiencies, or by the campaigner's dishonest attempt to win in political, business or other spheres of competition against an honest rival. However, if the mudslinging statements can be proved to be correct, mudslinging takes the moral dimension of an opponent's duty serving the greater good by exposing the weakness of the other candidate.

The public image of an entity can be defined as reputation, esteem, respect, acceptance of the entity's appearance, values and behaviour by the general public of a given territory and/or a social group, possibly within time limits. As target groups of public and their values differ, so negativity or positivity of a public image is relative; thus, to be successful, negative campaigning has to take into account current values of the group it addresses. The degree of strictness in practicing the group's values as opposed to its tolerance for violating the norms has also to be taken into consideration.

There are a number of techniques used in negative campaigning. The most standard form of negative campaigning is campaign advertising that serves as an attack on an opponent's personality, record, or opinion. There are two main types of ads used in negative campaigning: attack and contrast.

Attack ads focus exclusively on the negative aspects of the opponent. There is no positive content in an attack ad, whether it is about the candidate or the opponent. Attack ads usually identify the risks associated with the opponent, often exploiting people's fears to manipulate. Because attack ads have no positive content, they have the potential to be more influential than contrast ads in shaping voters’ views of the sponsoring candidate's opponent. One of the most famous attack ads was Daisy Girl by the campaign of Lyndon B. Johnson that successfully portrayed Republican Barry Goldwater as threatening nuclear war. Common attack ad themes include painting an opponent as soft on criminals, dishonest, corrupt, or a danger to the nation. Another relatively common theme is attacking the other side for running a negative campaign.

Unlike attack ads, contrast ads contain information about both the candidate and the opponent. The information about the candidate is positive, while the information about the opponent is negative. Contrast ads compare and contrast the candidate with the opponent, juxtaposing the positive information about the candidate with the negative information of the opponent. Because contrast ads must contain positive information, contrast ads are seen as less damaging to the political process than attack ads.

Push polls are attacks disguised as telephone polls. They might ask a question like "How would you react if Candidate A was revealed to beat his wife?", giving the impression that Candidate A might beat his wife. Members of the media and of the opposing party are deliberately not called making these tactics all but invisible and unprovable.

Dirty tricks are also common in negative political campaigns. These generally involve secretly leaking damaging information to the media. This isolates a candidate from backlash and also does not cost any money. The material must be substantive enough to attract media interest, however, and if the truth is discovered it could severely damage a campaign. Other dirty tricks include trying to feed an opponent's team false information hoping they will use it and embarrass themselves.