An ox (PL: oxen, ), also known as a bullock (in BrE, AusE, and IndE), is a bovine trained and used as a draft animal. Oxen are commonly castrated adult male cattle; castration inhibits testosterone and aggression, which makes the males docile and safer to work with. Cows (adult females) or bulls (intact males) may also be used in some areas.

Oxen are used for plowing, for transport (pulling carts, hauling wagons and even riding), for threshing grain by trampling, and for powering machines that grind grain or supply irrigation among other purposes. Oxen may be also used to skid logs in forests, particularly in low-impact, select-cut logging.

Oxen are usually yoked in pairs. Light work such as carting household items on good roads might require just one pair, while for heavier work, further pairs would be added as necessary. A team used for a heavy load over difficult ground might exceed nine or ten pairs.