Ice Release (氷遁, Hyōton, Viz: Haku's Secret Arts of Water, English TV: Ice Style) is the advanced nature kekkei genkai of the Yuki clan, and allows the users to combine wind and water-based chakra to create ice which they can manipulate through willpower alone. The ice Haku created was resistant to fire-based attacks, only melting slightly when coming into contact with Sasuke's flames. Using his special ability, Haku developed the Demonic Mirroring Ice Crystals, which allowed him to create any number of floating mirrors made of ice to use as a shield or trap an opponent.
Haku mentioned that having nearby water is an advantage, as he can simply freeze that water to create ice.
Without the Kekkei Genkai
In the first Naruto movie, several of the Yukigakure ninja also had the ability to use Ice Release techniques. However, this was not the product of a similar kekkei genkai, as demonstrated by Kakashi's ability to replicate one of these techniques with his Sharingan. In addition, unlike Haku, who could create his own ice, the Ice Release techniques used in the movie required the users to manipulate already existing ice and seems to melt at a much easier level than the ones Haku used. Another notable difference is that they can also manipulate snow. The Yukigakure ninja most commonly used the Dog hand seal to do this. Dotō Kazahana, in particular, manipulated a special type of snow that is black in colour.
In the Land of Vegetables Arc, the main villain Renga also used a technique using ice. He could crystallise the water vapour around him into ice so transparent that it would be practically invisible to the naked eye. However, this technique was never mentioned to be an Ice Release technique.