Wood Release (木遁, Mokuton; English TV "Wood Style") is an advanced nature kekkei genkai formed through simultaneous use of earth and water-based chakra natures to create wood, or complete trees. This ability can also be used to create other aspects of trees, such as seeds or even flowering plants. Wood Release techniques can be produced from anywhere, including the user's body, as the user's chakra is literally converted into a source of life. Wood Release Techniques (木遁の術, Mokuton no Jutsu) are commonly affiliated with the Snake seal.
The ability originated with Hashirama Senju, as no other member of his clan was known to possess it. His ability to use this technique was one of the reasons he was given the title of the First Hokage, and with Wood Release Secret Technique: Nativity of a World of Trees he created the foundation of Konohagakure. This technique also allowed him to completely reshape battlefields to his advantage. A highly coveted ability, several people have tried to replicate his power, with a few achieving weaker versions of it through experimentation with Hashirama's cells. As Obito Uchiha noted, Wood Release is very hard to control due to the sheer life force that his cells possess, and they can potentially overwhelm any who are infused with them. Danzō Shimura demonstrated this when, after his chakra levels were depleted, he almost turned into a tree as the cells overpowered him. It is also noted that those who integrate these cells with themselves grow Hashirama's visage on their body. The first person to attempt to make Hashirama's power his own was his rival, Madara Uchiha. Having used their confrontation at the Valley of the End to acquire a portion of his DNA, Madara later applied it to the wounds he sustained. As a result, Madara was able to perform Wood Release techniques, which he demonstrated upon his reincarnation during the Fourth Shinobi World War. Madara also used Hashirama's cells, along with the Demonic Statue of the Outer Path, to create a living clone of Hashirama. From this clone, Madara was able to produce various artificial humans, each of which was capable of performing a weaker version of Hashirama's Wood Release. After being mortally wounded during his mission at Kannabi Bridge, Obito Uchiha was repaired with the genetic material from the living clone by Madara, giving him the ability to use Wood Release as well.
Orochimaru, another who desired the First Hokage's abilities, injected Hashirama's DNA into sixty test subjects, and out of the sixty only Yamato survived. With his own DNA overridden, Yamato gained the ability to use Wood Release. Orochimaru also performed a similar procedure on Danzō Shimura by implanting the First's cells in his right arm. While Danzō is capable of using this power, it appears Danzō's version is much cruder and causes a much more significant drain of chakra with each usage, causing Danzō to avoid using it as much as possible. Orochimaru also kept a sample of Hashirama's DNA and later used it to reincarnate the First Hokage himself to fight for him during the Invasion of Konoha. Orochimaru himself would later acquire this coveted ability after taking over the body of a spore clone. 
A derived technique of the Wood Release is the Hokage-Style Sixty-Year-Old Technique — Kakuan Entering Society with Bliss-Bringing Hands. This technique produces a seal "sit" (座) on the user's right hand that can suppress a tailed beast's influence over its jinchūriki. This is done by producing wooden dragons from the ground that attach to the host and force the tailed beast's chakra to recede. Hashirama's necklace aided in this technique's execution, but its exact purpose was unclear. After Naruto destroyed the necklace, however, Yamato implied that he could no longer suppress the Nine-Tailed Demon Fox's influence. Nevertheless, during Naruto's training to control the Nine-Tails at the Falls of Truth, when he was transforming, Yamato stated that he would try to suppress the beast. Whether or not this would have worked was never seen due to the transformation stopping through other means.
After reviving the Ten-Tails in an incomplete state, Madara and Obito were able to improve their control of the beast through the use of Hashirama's cells. Obito also demonstrated the ability to channel his Wood Release techniques through the Ten-Tails' body while attached to it.