The Stargates, also called the Astria Porta in Ancient and the Chappa'ai in Goa'uld, are a series of devices, built by the Ancients, that create artificial subspace wormholes, allowing for near-instantaneous transportation between two distant points in space. The Stargates are often considered to be the Ancients' greatest creation, and so the Ancients are often called the Gate Builders. The Ancients, the Asurans, the Tollan, and the Ori are the only known races that have managed to build Stargates.

The original Stargate design was invented by an Alteran named Amelius, from an idea he formulated the night before the Alterans left their home galaxy for the Milky Way. It is unknown if he actually built the first of the Stargate Network. They are among the oldest examples of Ancient technology found in the Milky Way galaxy; the Stargate found in Antarctica on Earth has been estimated to be over 50 million years old, while the Stargates used in the "Destiny mission" are even older. (SG1: "The Ark of Truth")

 

The Ancients placed Stargates on thousands of worlds across several galaxies. They have long since reached Ascension, but the network remains accessible to any with the knowledge of how it works, and continues to be a convenient form of travel for many races. Some races, such as the Goa'uld, grew their ways of life around the gates, which became integral to the functioning of their culture.

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In turn, most races developed their own names for the Stargates. The Ancients called them "Astria Porta". The English word "Stargate" is a calque of the Goa'uld word "Chappa'ai", courtesy of a direct translation by Daniel Jackson, and "Chappa'ai" is itself a calque of "Astria Porta". The K'Tau call their Stargate "the annulus". In the Pegasus Galaxy, villagers know them as Rings of the Ancestors and variations thereof. They are also commonly referred to as simply "the ring" or "the gate". The Wraith call it the Portal.

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​Although Stargates are present on many planets, most of the races which use them are relatively primitive, and view the technology as divine in nature, as evidenced by such names as "Ring of the Gods" and "Circle of Darkness". In many cases the references to gods or evil in the names come from the Goa'uld, or in the Pegasus galaxy, legends of the Ancients or their present use by the Wraith. (SG1: "The First Commandment", "Demons", "Memento")

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​The Stargate creates a stable, artificial wormhole between itself and another Stargate, allowing near-instantaneous travel from the dialing gate to the destination gate, but not vice versa. When activated, a Stargate produces a violent burst of energy known as an unstable vortex or "kawoosh". This is due to the large amount of energy needed to form a stable wormhole, while keeping one open is much less power-intensive. This event will destroy any matter it comes into contact with; however, if the event horizon is blocked to within a few microns, the vortex will be suppressed. Technologies such as the iris on Earth's Stargate can achieve this. The vortex settles into the event horizon, nicknamed the puddle for its liquid appearance. Travelers enter through the event horizon, which dematerializes them for transport through the wormhole, to be reassembled on the other side. The Stargate will remain open so long as matter or energy continues to pass through it, to a maximum of 38 minutes. Beyond this point, massive amounts of power are needed to sustain a wormhole, which ordinary sources cannot provide.

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​Travel through a Stargate is strictly one-way: from the dialing gate to the receiving gate. This is not a limitation of the wormhole, but of the technology; wormholes will transmit anything that enters them, but no solid matter could survive the process. Thus, each gate in the pair takes on a specific role: the dialing gate converts the traveler into its most basic components (sub-atomic particles) and transmits it, while the receiving gate reassembles the transmitted matter back into its original form. Doing the reverse is not only fatal for the traveler, but would just result in the dialing gate deconstructing the object upon arrival, converting it into energy. It is unknown what would happen if someone entered the Stargate via the 'back' rather than the 'front'; Teal'c once stated that he knew someone who attempted that on one occasion and that his death was "most unpleasant", but further details are unknown. (SG1: "A Hundred Days", " Survival of the Fittest")