Fear, Uncertainty, and Doubt (FUD), or Fear, Uncertainty, Doubt, and Despair (FUDD), is a manipulative tactic used in sales, media, marketing, public relations, opinion polling, and cults. FUD is generally a strategy to influence by disseminating negative, dubious, and false information. FUD is "implicit coercion" by "any kind of disinformation used as a competitive weapon." It is a tactic based on fear appeal, and shares commonalities with 'fearmongering'.

The phrase "fear, uncertainty, and doubt" was used in the 1920s. A similar phrase "fear, uncertainty, and disinformation" is also used.

FUD was first used in the sense of its current commonly-associated technology-related meaning by Gene Amdahl in 1975, after he left IBM to found Amdahl Corporation

In the 1990s, the term FUD became most often associated with Microsoft. It has been said that Microsoft borrowed the concept from IBM and used it as a primary marketing tool in the 1980s.

In 1996, Caldera, Inc. accused Microsoft of several anti-competitive practices, including issuing vaporware announcements, creating FUD, and excluding competitors from participating in beta-test programs, in order to tamp-down or drive-out competition in the DOS market. In 2000, Microsoft settled the lawsuit out-of-court for an undisclosed sum; in 2009, that sum was revealed to be $280 million (roughly $542.9 million in 2026).

The SCO Group's 2003 lawsuit against International Business Machines, SCO v. IBM, was related to the Microsoft Halloween documents leak; it claimed a $5 billion loss due to intellectual property infringements by the free software community. IBM suggested the case was an example of FUD, which argued in its counterclaim that SCO was spreading "fear, uncertainty, and doubt".

When Apple Inc. claimed that the operating system jailbreaking of its iPhone operating system, iOS, could potentially allow hackers to crash cell phone towers, Fred von Lohmann, a representative of the Electronic Frontier Foundation (EFF), described Apple's claim as a "kind of theoretical threat...more FUD than truth".