Eight Branches Technique

This is Orochimaru's greatest and strongest technique. Using the "power of reincarnation" possessed by the White Snake as an intermediary, he can transform into a giant white serpent with eight heads and eight tails. The serpent boasts a giant body, even larger than that of Manda, who is feared as the "strongest colossal serpent". Just by crawling on the scales of it's abdomen it was able to trample the Uchiha hideout, and can attack most things without fear.

When using this technique, Orochimaru can emerge from the mouth of one of the heads and use his Kusanagi Sword to attack, even without a host.

The third databook says this technique transcends the "Snake", and becomes like a "Dragon God".

Trivia

 * The name of this jutsu comes from the legendary snake Yamata no Orochi, a monstrous eight-headed and eight-tailed snake that was destroyed by the god Susanoo-no-Mikoto. This is a reference to how Itachi's Susanoo killed the serpents produced by this technique.
 * In Naruto Shippūden: Ultimate Ninja Storm 2, the eight snake's heads can unite to create a devastating energy attack that was powerful enough to temporarily overwhelm the defenses of Susanoo.