The Byakugan (白眼; Viz "Evil Eye" or "All Seeing white Eye"; Literally meaning "White Eye"; ) is a genetic trait that is shared amongst the members of the Hyuga Clan. Those that inherit the blood of this clan have almost featureless white eyes (Neji's and Hinata's eyes seem to have tints of lavender and blue-gray, respectively). Although it is not stated directly, it is assumed that all members of the Hyuga family possess the Byakugan. It is a common, but not proven belief that the Sharingan is a genetic offshoot of the Byakugan.
The Byakugan is the primary focus of the Hyuga's special arts. When the Byakugan is activated, their pupils become more distinct and the veins near their temples bulge. Once active 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. They also have the ability 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. In Part I, Neji Hyuga was able to see an area of 50 meters, but later he increases his visual range to at least 800 meters. During the hunt for either of the Uchiha brothers, Hinata was shown to be able to view Amaterasu's flames and the chakra in the area from ten kilometers away.
However, one of the greatest uses of the Byakugan is the ability to see the chakra circulation system inside of another's body. The Byakugan has also shown the ability to see what a person's chakra type is, by looking into someone's chakra points. 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.
Particularly skilled users of the Byakugan, which appear only rarely, such as Neji Hyuga, can take the Gentle Fist style one step further. Along the keirakurei are 361 pinprick-sized nodes called Tenketsu, or chakra points. When struck, these tenketsu will seal off, which close the opening points from which chakra is emitted. Thus, with precision, all those points along the victim's body can be sealed, stopping the chakra flow to those areas. Most of the Hyuga clan cannot even perform this because the Tenketsu are too small to see. Neji Hyuga is the rare exception, having taught himself the ultimate Hyuga technique, Eight Trigrams Sixty-Four Palms, along with Hinata Hyuga, who was not able to do 64 palms like Neji, but she is able to do Eight Trigrams 32 Palms, an slightly weaker version of Neji's, albeit only in the anime. Able to strike without force, and yet do more damage to a ninja than some of the most powerful Ninjutsu, the Gentle Fist is the greatest Taijutsu style known in all of Konoha.