The Holodeck is a fictional device from the television franchise Star Trek which uses "holograms" (projected light and electromagnetic energy which create the illusion of solid objects) to create a realistic 3D simulation of a real or imaginary setting, in which participants can freely interact with the environment as well as objects and characters, and sometimes a predefined narrative.

From a storytelling point of view, the holodeck permits the introduction of a wide variety of locations and characters, such as events and persons in the Earth's past, or imaginary places or beings, that would otherwise require the use of plot mechanisms such as time-travel or dream sequences.

[3] Prior to Star Trek, science-fiction writer Ray Bradbury wrote about a technology-powered "nursery", a virtual reality room able to reproduce any place one imagines, in his 1950 story "The Veldt".

Hungarian-British physicist Dennis Gabor received the Nobel Prize in Physics in 1971 "for his invention and development of the holographic method", work done in the late 1940s.

The first practical optical holograms recording 3D objects were made in 1962 by Yuri Denisyuk in the Soviet Union and by Emmett Leith and Juris Upatnieks at the University of Michigan in the United States.

The opening scene of the 1994 film Star Trek Generations features a holodeck simulation of a sailing ship including a surrounding ocean.

The metaphysical questions raised by self-aware simulated characters are explored in several Star Trek episodes, including "Elementary, Dear Data", in which a holodeck recreation of Professor Moriarty becomes self-aware and demands a life outside of the holodeck; unable to meet his demands, Captain Picard saves Moriarty's program against the day when that will be possible.

In Star Trek: Deep Space Nine, patrons of Quark's bar pay for hourly rentals of "holosuites" and pornographic holoprograms.

Star Trek: Voyager also introduces alien beings known as photonic lifeforms who believe holodeck programs are real, rather than computer-driven simulations.

The Star Trek: The Next Generation episode "The Big Goodbye" (airdate January 11, 1988), featuring a story set in the holodeck, was honored with a Peabody Award in recognition of its "new standard of quality for first-run syndication".