Bell bottoms are trousers that become more wide from the knees downwards.

It is believed that bell-bottom pants were introduced in 1817 to sailors working on deck. The flare at the end of the pant leg allowed them to be rolled up more easily than normal straight-legged pants. The bell-shaped leg also made the pants easier to remove in a hurry when forced to abandon ship or when washed overboard. The pants may also be knotted at the legs to be used as a life preserver. Absurdly wide hems became fashionable in the 1960s, both for men and women.

If a person looks at a pair of bell-bottoms from front or behind, it has the form of a bell or trumpet. Bell-bottoms are sometimes worn by carpenters in order to prevent dust from getting into their shoes. In the modern fashion scene, bell-bottoms were most popular in the 1960s and 70s. They become popular again in 1990s in a reincarnation known as "flares", worn mostly by women.