The semicircular canals are curved tubes, projecting from and attached to the utricle of the inner ear of vertebrates, which serve as the primary organ of balance (see vestibular sense).

The three looped semicircular canals are set at right angles to each other and are filled with fluid (endolymph). Angular acceleration (for example, due to rapid turning) of the animal in any direction generates currents in the fluid along the corresponding canal. These currents are detected by fine projections from sensory cells in a swelling, called an ampulla, that lies at one attachment point of each canal. The sensory nerves communicate the information they receive to the brain via the auditory nerve.