The Byakugan (白眼; Literally meaning "White Eye", Meaning "All Seeing White Eye") is the dōjutsu kekkei genkai of the Hyūga clan. It is one of the first three great dōjutsu, along with the Sharingan and the Rinnegan.
Those that inherit the blood of this clan have almost featureless white eyes. When the Byakugan is activated, the user's pupils become more distinct, and the veins near their temples bulge. It also appears that unlike the other two dōjutsu, all members of the clan possess and can use the kekkei genkai from birth, as opposed to needing to awaken it.
The first ability of the Byakugan gives the user a near 360º field of vision, except for one blind spot at the back of the neck above the third thoracic vertebra. The second ability is being able to see through solid objects, and can use a degree of telescopic sight. The distance and the degree of telescopic sight varies from person to person, and can be improved. However, the Byakugan cannot see through certain barriers, such as sealing barriers.
The third and one of the greatest uses of the Byakugan is the ability to see chakra, chakra flow as well as the chakra circulation system inside the body with great detail. It is from this particular ability that they are able to employ their ultimate attack style: Gentle Fist. Unlike the Strong Fist, which is focused on external injuries, the Gentle Fist style focuses on internal injuries. Each strike, when placed correctly, strikes along the chakra pathway system, which is the network of vessels that carry chakra. This network is closely intertwined with the functioning of the body's organs, and so, when the keirakukei take damage, the organs suffer as well. There is no defense against the Gentle Fist, since one cannot train one's internal organs to become stronger. The only possible defense is to stop the Gentle Fist's hits from connecting. Also, like the Sharingan and Rinnegan, the Byakugan's ability to see chakra and its flow allows the user to detect chakra sealed barriers. It was also shown in the anime that the Byakugan can also discern a transformation and a real person using the eye's ability to see chakra.
Particularly skilled users of the Byakugan can take the Gentle Fist style one step further. Along the keirakurei are 361 pinprick-sized nodes called tenketsu, or chakra points. When struck, the Byakugan user can choose to either seal, or forcibly open these tenketsu, thus giving the user complete control over their opponent's chakra system. So, with precision, all those points along the victim's body can be sealed, stopping the chakra flow to those areas. Able to strike without force, and yet do more damage to a ninja than some of the most powerful ninjutsu, the Gentle Fist has been labeled as the greatest taijutsu style known in all of the elemental nations.