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The Holtzman effect is a fictional scientific phenomenon in the Dune universe created by Frank Herbert, beginning with the 1965 novel Dune. The effect is never explained in detail, but it makes (among other things) defensive force shields and instantaneous space travel possible.

Frank Herbert was inconsistent with the spelling of "Holtzman," resulting in the variant spellings "Holtzmann" (1976's Children of Dune) and "Holzmann" (1985's Chapterhouse: Dune). This may be intentional, as Herbert mutated other words and names over the several millennia the Dune series spans, such as the change of "Arrakis" to "Rakis" and "Caladan" to "Dan" beginning with Heretics of Dune (1984).

According to the Legends of Dune prequel trilogy by Brian Herbert and Kevin J. Anderson (2002–2004), the Holtzman effect is named after the scientist who discovered it, Tio Holtzman (though for many of its applications, Holtzman in fact takes credit for the mathematical theories of his assistant, Norma Cenva).

In Terminology of the Imperium, the glossary of the novel Dune, Frank Herbert provides the following definition:

SHIELD, DEFENSIVE: the protective field produced by a Holtzman generator. This field derives from Phase One of the suspensor-nullification effect. A shield will permit entry only to objects moving at slow speeds (depending on setting, this speed ranges from six to nine centimeters per second) and can be shorted out only by a shire-sized electric field.

In Dune, the technology has been adapted for reliable use in personal defensive shields which permit penetration only by objects that move below a pre-set velocity.Paul Atreides notes in Dune, "In shield fighting, one moves fast on defense, slow on attack ... Attack has the sole purpose of tricking the opponent into a misstep, setting him up for the attack sinister. The shield turns the fast blow, admits the slow kindjal!" It is further noted in the same chapter that the field forms a defensive bubble about the body.

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