Code Geass: Lelouch of the Rebellion (Japanese: コードギアス 反逆のルルーシュ, Hepburn: Kōdo Giasu: Hangyaku no Rurūshu), often referred to as simply Code Geass, is a Japanese anime television series produced by Sunrise. It was directed by Gorō Taniguchi and written by Ichirō Ōkouchi, with original character designs by Clamp. Set in an alternative timeline, it follows the exiled prince Lelouch Lamperouge, who obtains the "power of absolute obedience" from a mysterious woman named C.C.. Using this supernatural power, known as Geass, he leads a rebellion against the rule of the authoritarian Holy Britannian Empire, commanding a series of mecha battles.

Code Geass was broadcast in Japan on MBS from October 2006 to July 2007. Its sequel series, Code Geass: Lelouch of the Rebellion R2, ran as a simulcast on MBS and TBS from April to September 2008. The series has also been adapted into various manga and light novels, with the former containing alternate scenarios from the TV series.

Initiation, Transgression, and Glorification, a three-part compilation film recapping the events of both anime series' seasons while also altering storylines for various characters and establishing an alternate universe, was released between 2017 and 2018. A new original film titled Code Geass Lelouch of the Re;surrection, taking place after the Zero Requiem of the film trilogy's alternate universe, was released in theaters in February 2019. Code Geass: Rozé of the Recapture, an anime film series set in the same alternate universe, was announced in December 2020 as part of a 10-year plan. On 7 December 2024, after the screening of Code Geass: Rozé of the Recapture, series producer Taniguchi revealed that multiple sequels are being produced.

Bandai Entertainment licensed most parts of the franchise for English release in December 2007, airing the series English-dubbed on Adult Swim in the United States. Most manga and light novels have also been published in North America by Bandai.

Code Geass has been well received in Japan, selling over a million DVD and Blu-ray discs. Both seasons have won several awards at the Tokyo International Anime Fair, the Animage Anime Grand Prix, and the Animation Kobe event. The series received critical acclaim for its story, voice acting, large audience appeal, the conflicts among its main characters, and the moral questions it presented. It is considered to be one of the best anime series of all time.

In an alternative timeline, the world is divided into three superpowers (similar to the world of Nineteen Eighty-Four by George Orwell): the Holy Britannian Empire (the Americas; also called Britannia), the Chinese Federation (Asia), and the Europa United (Europe and Africa). The story takes place after the Holy Britannian Empire's conquest of Japan on August 10, 2010, a.t.b., by means of Britannia's newest weapon, the "Autonomous Armored Knight," or "Knightmare Frame." In turn, Britannia effectively strips Japan and its citizens of all rights and freedoms and renames the country Area 11, with its citizens referred to as Elevens.

The point of divergence for this timeline appears to be that during the reign of Elizabeth I, though the queen remained unmarried and bore a son (the fictional ancestor of the Britannian Emperors, Henry IX). However, several alternative timelines exist in the Code Geass universe, and the point of divergence may differ between each. The most common point of divergence in all timelines is in the Code Geass universe, with Julius Caesar's invasions of Britain between 55 and 54 BC ending in failure when the British Celts united under Alwin the First. They forced the Romans out and established the First United British Kingdom in 54 BC, which became the first year of the Britannian Calendar (1 a.t.b, first year of Ascension Throne Britannia, with 55 BC as 1 b.t.b., the first year Before Throne Britannia). While other Roman invasions had been followed, by 43 a.t.b.(12 BC) Britannia was recognized as an independent kingdom by the Roman Empire. As such, while many events in the Code Geass universe share similar dates with actual history, in truth they take place about half a century earlier (as with the French Revolution of 1789 a.t.b., or 1734 AD). Almost all timelines share a version of the Geass Order/Cult/Directorate, an organization that controls and uses Geass users and abilities and which is heavily involved with the Britannian Imperial Family.

Lelouch vi Britannia is an exiled Britannian prince, the son of Emperor Charles zi Britannia and his royal consort Marianne vi Britannia. Lelouch has a younger sister, Nunnally Vi Britannia. Marianne was brutally murdered in the palace, and Nunnally, who witnessed the murder of their mother, was so traumatized that she lost her sight, and stray bullets to her lower body took away her ability to walk. Lelouch is furious with his father, believing he failed his mother and sister by turning a blind eye to their mother's death and failing to pursue their mother's killer.