Tailed Beast Control

Throughout the series, several shinobi, jinchūriki or not, have demonstrated the ability to gain control of one or more of the nine tailed beasts. The cause and effect of this control varies between those capable of doing it.

Jinchūriki
The jinchūriki have the potential to control their tailed beasts' power through sheer willpower, but requires a lot of training in order to retain it. According to Gerotora, it is implied that the tailed beasts' power consists of two parts: chakra and will. Whenever a jinchūriki draws out a certain amount of his/her tailed beast's chakra, its will will fuse along with it, to which it involves a psychological struggle between the two as the jinchūriki transforms deeper into his/her tailed beast's forms. If a jinchūriki were to become completely succumbed to its influence, the seal would break and the tailed beast would be released. For a jinchūriki to have complete control, one must have something to fill in the void within their hearts to give them strength.

While some jinchūriki, such as Gaara, Yugito Nii, and Utakata (in the anime), had shown to use their tailed beasts' power to a certain degree, their control over it was lacking compared to Yagura, Killer B, and Naruto Uzumaki's, as they became the jinchūriki to have complete control. Upon their resurrection, all the previous jinchūriki have displayed remarkable control, as Yugito, Yagura, Rōshi, Han, Utakata and Fū were all able to partially manifest them by displaying one of their tails (two in Fū's case, which enabled her to fly), and enter into "Version 2"-like forms, further showcasing their tailed beasts' strength, and even fully transforming into their respective tailed beasts.

Once a jinchūriki becomes compatible with his/her tailed beast, the beast can act as his/her partner in battle. Advantages include not only making use of the tailed beast's considerable abilities and shapeshifting between its transformations, but also becoming immune to genjutsu, as the tailed beast can disturb its jinchūriki's chakra flow to break genjutsu. However, to achieve that, the tailed beast and its jinchūriki must have agreements of trading certain amounts of their own chakra, otherwise, if a jinchūriki has complete control over the tailed beast's chakra but doesn't possess its own cooperation, the transformation will result in failure, and the tailed beast will then gradually consume its jinchūriki's own chakra whenever he/she uses the tailed beast's chakra, which can kill the jinchūriki.

Non-Jinchūriki
Hashirama Senju, the First Hokage, could completely control the tailed beasts by using his Hokage-Style Sixty-Year-Old Technique — Kakuan Entering Society with Bliss-Bringing Hands, which utilises the power of his Wood Release kekkei genkai to forcibly suppress the tailed beasts' chakra. Yamato would later also acquire this power due to his genetic alteration, however by his own admission, to a lesser extent.

While both Madara Uchiha and Tobi could fully control the tailed beasts by using the Sharingan, Sasuke Uchiha at first used his Sharingan to only suppress a small amount of Kurama's chakra within Naruto's subconscious. Tobi's method of control soon changed when he gained the Rinnegan, using the Outer Path's abilities to bind the tailed beasts with special chains of chakra.

When Tobi learned of Danzō's use of both Wood Release and Sharingan, he speculated that Danzō intended to control Kurama.

In the anime, Yūkimaru was able to partially control Isobu, the former tailed beast of Yagura.