The Byakugan is the dōjutsu kekkei genkai of the Hyūga and Ōtsutsuki clans, inherited from Kaguya Ōtsutsuki. It is regarded as one of the "Three Great Dōjutsu", the others being the Sharingan and the Rinnegan.
This dōjutsu usually is manifested as very distinctive eyes, characterised by their enlarged and featureless white irides (though the anime tends to portray them as a light shade of lavender) with no visible pupils. While active, the pupils become more distinct and the veins near their temples bulge. Unlike other dōjutsu, the Byakugan is normally available to its users from birth, and on rarer occasions, the dōjutsu can be awakened. Himawari Uzumaki, a descendant of the Hyūga clan through her mother, generally has blue eyes. When her Byakugan is activated, she gains the characteristic white, featureless eyes of her ancestors.
In the novel adaptation, it was shown that a Hyūga descendant of a more diluted bloodline may end up only awakening this dōjutsu in a single eye.
The Byakugan's abilities have left it highly coveted, as evidenced by other villages' attempts to steal it; Kumogakureused various machinations to obtain a Byakugan during the "Hyūga Affair". Ao of Kirigakure is the only foreign power known to have obtained a Byakugan from a Hyūga he defeated and he goes to great lengths to protect it; when Danzō Shimura, a loyal extremist of Konoha, finds out about this, he goes to similar lengths to retrieve or destroy it. Unlike other dōjutsu, transplanted Byakugan can be activated and deactivated at will. In order to reduce the probability of their eyes falling into enemy hands, the main house of the Hyūga place cursed seals onto the foreheads of branch house members which, among other things, seals away the Byakugan upon their death.
In the manga, after absorbing Kinshiki Ōtsutsuki's power, Momoshiki Ōtsutsuki's Byakugan takes a gold colour.
The Byakugan gives the user a near 360º diameter field of vision, with one blind spot at the back of the neck above the first thoracic vertebra. The range of this vision varies between users and can be improved with training: for example, Hinata Hyūga as a genin could see targets 50 metres away; by age 18, she can see targets 20 kilometres away. Its vision can penetrate through any solid objects or obstructions, and likewise remains unaffected by blinding interferences, though certain barriers may distort the Byakugan's perception. The Byakugan is able to follow high-speed movements, which allows the wielder to analyse their opponent's actions, and allows the user to predict and better react to them. In the anime, the Byakugan is shown magnifying in on small targets and seeing infrared to detect a target through their body heat. In the anime, a powerful enough user can see through one's thoughts and feelings, which Kaguya perform to such a level that even Hamura proved incapable of repelling with his Byakugan. It can also emit powerful chakra pulses to subdue an opponent.
The Byakugan is able to see chakra to a higher degree than the Sharingan, such as identifying where a person's chakra signature originates from. It can discern certain types of clones from the real person. Its ability to see chakra is acute enough to see the chakra pathway system and the 361 tenketsu that run along it. The Hyūga have devised a fighting style known as the Gentle Fist to take advantage of this ability, wherein they strike an opponent's tenketsu to either seal or forcibly open them, thus giving the user complete control over their opponent's chakra.
The Byakugan can also decipher whether or not genjutsu is being used on either the wielder or others. According to Hagoromo, the Byakugan can also be used to extend the range of genjutsu; Kaguya indeed used her Byakugan in tandem with the Rinne Sharingan to cast the Infinite Tsukuyomi on nations.
In the manga, Momoshiki could use his Byakugan to read the fate of other people, though it didn't allow him to see his own fate.
Prolonged use of the Byakugan causes severe but temporary eye-strain, leaving wielders unable to properly perceive targets. In the anime, it was shown that once manifested, the Byakugan will automatically activate if the user is stressed enough from confrontation.
When the Byakugan of a Hyūga clan member is combined with the chakra of an Ōtsutsuki clan member descended from Hamura Ōtsutsuki, over a certain period of time it evolves into the Tenseigan. When Toneri Ōtsutsuki gains the Tenseigan by taking the eyes of Hanabi Hyūga, he accesses the Tenseigan Chakra Mode, granting him Truth-Seeking Balls and physical enhancements similar to the Nine-Tails Chakra Mode. Shisui Uchiha II was able to combine the Tenseigan Chakra Mode with His Six Paths Sage Mode, and Tailed-Beast Mode, making more adept at Fighting than Kaguya and Hamura. This also granted him the Ability to take on a Form Similar to Hamura as a result of Possessing Half of Hagoromo's Chakra and the Byakugan, with is Uchiha and Senju Blood through his Paternal Line and his Otsutsuki Heritage through his Maternal Line of the Hyuga.
The Tenseigan also provides the ability to control gravitational forces and other telekinetic-like abilities. The Tenseigan can lose its power and revert to the Byakugan if weakened enough in battle. Shisui Uchiha II's Tenseigan Took on a Form Similar to his Rinnegan, that his Tenseigan took on an Additional Tomoe pattern though was forced back to Normal Byakugan when he had lost too much Chakra.