Red vs. Blue, often abbreviated as RvB, is an American web series created by Burnie Burns with his production company Rooster Teeth. The show is based on the setting of the military science fiction first-person shooter series and media franchise Halo. It is distributed through Rooster Teeth's website, as well as on DVD, Blu-ray, and formerly on the El Rey Network and Netflix. The series initially centers on two opposite teams fighting in an ostensible civil war—shown to actually be a live fire exercise for elite soldiers—in the middle of Blood Gulch, a desolate box canyon, in a parody of first-person shooter video games, military life, and science fiction films.

Initially intended to be a short series of six to eight episodes, the project quickly and unexpectedly achieved significant popularity following its premiere on April 1, 2003. The series consists of eighteen seasons and five mini-series. Red vs. Blue was the second longest-running animated webseries of all time, behind Homestar Runner, until its conclusion in 2020. The series concluded with the feature-length movie Red vs. Blue: Restoration, originally intended to be a nineteenth season prior to the shutdown of Rooster Teeth, which was released on May 7, 2024.

Red vs. Blue emerged from Burnie Burns' voice-over gameplay videos of Bungie's FPS video game Halo: Combat Evolved. The series is primarily produced using the machinima technique of synchronizing video footage from a game to pre-recorded dialogue and other audio. Footage is mostly from the multiplayer modes of Halo: Combat Evolved and its followups on the Xbox consoles.

The series has been generally well-received. Praised for its originality, the series has won four awards at film festivals held by the Academy of Machinima Arts & Sciences. It has also won the award for "Best Animated Web Series" from the International Academy of Web Television (IAWTV). It also won a 2013 Webby Award for Animation, as well as nominated in 2014. It has been credited with bringing new popularity to Machinima, helping it to gain more mainstream exposure, and attracting more people to the art form. Graham Leggat, former director of communications for Lincoln Center's film society, described Red vs. Blue as "truly as sophisticated as Samuel Beckett". Rooster Teeth has created episodes, some under commission from Microsoft, for special events. The voice actors from Red vs. Blue appear in cameos for Halo 3 and Halo 4. The series is also referenced in Halo: Reach and Halo Infinite.