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The Halo Array is a group of fictional megastructure and superweapon in the Halo science-fiction franchise, consisting of ringworlds known as Halos built by a structure known as the Ark. They are referred to as "Installations" by their artificial intelligence caretakers, and were created by an ancient race known as the Forerunners. The series' alien antagonists, the Covenant, refer to the Halos as the "Sacred Rings", believing them to form part of a greater religious prophecy known as "The Great Journey". In the games' stories, the Forerunners built the Halo Array to contain and study the Flood, an infectious alien parasite. The rings act together as a weapon of last resort; when fired, they kill all sentient life in the galaxy capable of falling prey to the Flood, thereby starving the parasite of its food. The battle to prevent their activation forms the crux of the plot progression for the first Halo trilogy of games.

Each Halo features its own wildlife and weather. The constructs resemble Iain M. Banks' Orbital concept in shape and design. The structure on which Halo: Combat Evolved takes place was initially intended to be a hollowed-out planet, but was changed to its ring design later in development; a staff member provided "Halo" as the name for both the ring and the video game after names such as Red Shift were suggested.

The term "megastructure" refers to artificial structures where one of three dimensions is or larger. The first use of a ring-shaped megastructure in fiction was Larry Niven's novel Ringworld (1970). Niven described his design as an intermediate step between Dyson sphere and planets – a ring with a radius of more than and a width of ; these dimensions far exceed those of the ringworlds found in the Halo series, which have radii of The Halos are closer in proportion to a Bishop Ring, an actual proposed space habitat first explained by Forrest Bishop, though the proportions of the Halos do not exactly match up with Bishop's idea or more accurately the bigger Orbital. As seen in the games, Halo installations feature a metallic exterior but an inner surface filled with an atmosphere, water, plant life, and animal life. What appears to be docking ports and windows dot the exterior surface, suggesting that a fraction of the ring structure itself is hollow and used for maintenance, living, and power generation.

Before the title of the game that would become Halo: Combat Evolved was announced, while development was in its early stages, the megastructure on which the game took place was a massive, hollowed-out planet called "Solipsis". As ideas evolved, the planet became a Dyson Sphere, and then a Dyson Ring. Some Bungie staffers felt the change to a ringworld was "ripping off Larry Niven", according to Bungie artist Paul Russel. Bungie employee Frank O'Connor wrote in a post on Bungie that "the specific accusation that we swiped the idea of a ring-shaped planet wholesale is not accurate", explaining that Bungie used a ringworld because "it's cool and therefore the type of thing a Forerunner civilization would build." The immense scale of the Dyson megastructures was shrunk for the Halos, as artist Mark Goldsworthy noted that they wanted players to be able to see the ring stretching into the sky and behold the scale of the ringworlds.

Installation 04 has not been a contender in any CBUB matches.