The Original Dojutsu that was said to evolved into the legendary Sharingan, still prominently used by Konoha's Hyuuga Clan.
When the Byakugan is activated, the users pupils become less distinct and the veins around their eyes bulge, indicating the blood pressure increases around the eyes. The user can then see in a near 360 degree area around their body, except for a 1 degree blind-spot located behind the neck along the spinal cord. The Byakugan eyes give their user a power similar to X-ray vision in a large radius. It allows them to see the chakra and the chakra flow in the bodies of others, and even enables them to see the chakra points with a high degree of training or natural talent. Its also gives them telescopic vision and even microscopic vision along with the gift of insight; however they cannot use the insight on themselves. Neji Hyuuga has been said to be have a visual range of 800 meters. Byakugan users also have the notable ability to project chakra from their body, being used to create punishing waves and protective shields. The Byakugan is noted to have greater vision and insight than the Sharingan. Unlike a transplanted Sharingan, a transplanted Byakugan can be activated and deactivated at will. This is demonstrated in Ao's battles.
An experienced Byakugan user can use their gift to temporarily close off an opponent's various flows of chakra with carefully placed chakra blows, rendering the opponent unable to move the part of their body that was struck. Not only that, but if they seal up the right chakra points, they can kill even the strongest person with just a few blows, as bodies require the flow of chakra to live. This is known as the gentle fist technique, which was developed to take advantage of the Byakugun. This technique requires a high degree of chakra control, and the bloodline itself seems to lend to the control of chakra in the Hyuuga, as they are able to see the flow and control it more easily.