Halo is a video game franchise developed by Bungie, but now owned and managed by Microsoft subsidiary 343 Industries. The franchise started with the military science fiction game Halo: Combat Evolved on the Xbox in 2001. Since then, the franchise has grown into a multi-billion dollar empire spanning video games, comic books, novels, anime, television and film.

Halo follows the story Master Chief John-117, a Spartan supersoldier, as he fights for humanity in an interstellar war against an alliance of aliens known as the Covenant. Master Chief is assisted by the artificial intelligence companion Cortana – a feature available in Windows Phone 8.1. The Flood is a parasitic alien life form that infect sentient life. As such, they're an enemy to both humanity and the Covenant.

The original Halo trilogy consists of three video games. The first was Halo: Combat Evolved, which launched on the Xbox in 2001. The second game was Halo 2, available for Xbox in 2004. The third installment of the original Halo trilogy concluded with Halo 3 on the Xbox 360 in 2007. The original trilogy follows the story and adventures of Master Chief and Cortana.

A series of video game spin-offs exist in the Halo franchise. They are Halo Wars, Halo 3: ODST, Halo: Reach and Halo: Spartan Assault.

Halo Wars is a real-time strategy game for the Xbox 360 developed by Ensemble Studios. Halo 3: ODST followed a group of Orbital Drop Shock Troopers and was released for the Xbox 360 in 2009. Halo: Reach was the final Halo game developed by Bungie, it launched for the Xbox 360 in 2010. Halo: Spartan Assault is a top-down shooter developed originally developed Windows Phone and Windows 8, but now available for Xbox 360 and Xbox One.

The Reclaimer Saga is the second trilogy with Master Chief as the main protagonist. It started with Halo 4 on the Xbox 360 in 2012. Halo 5: Guardians will be the second installment in the Reclaimer Saga and the first Halo game on Xbox One. It's expected to launch holiday 2015.

In addition to video games, there are numerous Halo projects in various media. Numerous books have been printed and are considered Halo canon. A line of comics has also been produced over the years as tie-ins to video game launches.

Halo is no stranger to live-action film. Small projects have been produced over the years as part of advertising campaigns for video game launches, but larger projects have been made or are in development.

Forward Unto Dawn was a live-action film and miniseries for the Halo 4. The film served as a backdrop to the story of Halo 4. Halo: Nightfall is a Halo digital feature being produced by Ridley Scott. It will be included in 2014's Halo: The Master Chief Collection. A Halo live-action television series produced by Steven Spielberg is set for a fall 2015 premiere on American premium cable network Showtime.

Halo is one of Microsoft's most-valuable entertainment IPs. The series has received both critical and commercial success.