Stargate productions center on the premise of a "Stargate", a ring-shaped alien device that creates a wormhole enabling personal teleportation to complementary devices located cosmic distances away. Under the control of the United States government, the Stargate discovered on Earth is kept a secret from the public. This allows storylines to present no contradiction between depicted events and reality, an effect compounded by setting Stargate in the present day, and depicting Earth accurately, with any unrealistic technology originating solely from alien civilizations. These extraterrestrial civilizations are however more often pre-industrial than scientifically advanced, and are almost invariably human. Together, this allows for stories predominated by human interaction in Earth-like environments, an unusual feature for a science fiction franchise.

In the story, this is explained as being the result of alien interference in Earth's distant past - the concept influenced by the theories of Erich von Däniken. Many ancient mythologies are shown to be the result of aliens who had visited Earth posing as gods by using their technology to give the impression of deific power. While some of these aliens had benign intentions, a race later known in Stargate SG-1 as the "Goa'uld" used Stargates to move slaves from Ancient Egypt to other habitable planets, simultaneously being responsible for the Egyptian religion and culture. Following a successful rebellion, they fled Earth, and the Stargate was buried and forgotten until modern times, when the United States acquired it following an archaeological dig. Rediscovering the function of the Stargate, the galaxy is begotten as a source of knowledge, as well as threats, and the attention of the Goa'uld is drawn once more to Earth.