Fear, uncertainty, and doubt (FUD) is a manipulative propaganda tactic used in technology sales, marketing, public relations, politics, polling, and cults. FUD is generally a strategy to influence perception by disseminating negative and dubious or false information and is a manifestation of the appeal to fear.

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

By 1975, "FUD" was appearing in contexts of marketing, sales, and in public relations:

One of the messages dealt with is FUD—the fear, uncertainty and doubt on the part of customer and sales person alike that stifles the approach and greeting.

FUD was used with its common current technology-related meaning by Gene Amdahl in 1975, after he left IBM to found Amdahl Corporation

FUD is the fear, uncertainty and doubt that IBM sales people instill in the minds of potential customers who might be considering Amdahl products.

In the 1990s, the term became most often associated with Microsoft. It has been said that Microsoft took the concept from IBM and used it as a primary tool in the 1980s.^{[better source needed]}

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 to destroy competition in the DOS market. In 2000, Microsoft settled the lawsuit out-of-court for an undisclosed sum, which in 2009 was revealed to be $280 million.