Bridles are key items from The Legend of Zelda: Breath of the Wild. Link can purchase the default Stable Bridle from stables upon registration, and equip them onto wild horses that he tames, along with saddles. Bridles have reigns allowing Link to control the horse more humanly, as he holds onto their mane to control unregistered bridleless horses when riding bareback.
Link can obtain other bridles as rewards in mini-games. The Traveler's Bridle can be obtained by using the amiibo Rune with the Link Rider amiibo of the Breath of the Wild series, though it is worn by Link's unnamed horse from a century prior which appears in three Recovered Memories cutscenes indicating Link owned one before the Great Calamity. The Monster Bridle can be purchased at the Fang and Bone using the shop's special Mon currency which can be obtained by sell monster parts to the owner Kilton. Link can change bridles at certain stables by talking to a female stable hand. However he must have fully bonded with a registered horse in order to change its bridle and must have obtained a different bridle from the initial set first.
However some horses such as the Giant Horse from the side quest "Hunt for the Giant Horse" or Epona, obtainable through the amiibo Rune, are equipped with special bridles upon registration that is unique to them and cannot be changed. However the stable hand will state that Epona will not like it. In the case of the Giant Horse, his size prevents Link from changing bridles as only its default one fits. However the White Horse can be equipped with any bridle or saddle though it receives the Royal Bridle from Toffa after taming and registering it as part of "The Royal White Stallion" side quest along with the Royal Saddle. The Extravagant Bridle and Knight's Bridle are prizes received in Horse related mini-games.
Unlike armor worn by Link, bridles are purely cosmetic, and do not affect a horse's stats or increase their defense. The sole exception is the Ancient Bridle ("The Champions' Ballad" DLC), which increases a horse's stamina meter by two spurs. (It is also claimed that the Knight's Bridle reduces damage, but this requires testing.)
List of bridles