A bong (also water pipe,"popper bottle", bubbler, moof) is a filtration device/apparatus generally used for smoking cannabis, tobacco, or other herbal substances.

In construction and function a bong is similar to a hookah, except smaller and more portable. A bong may be constructed from any air- and water-tight vessel by adding a bowl and stem apparatus (or slide) which guides air downward to below water level whence it bubbles upward ("bubbler") during use. To get fresh air into the bong and harvest the last remaining smoke, a hole known as the "carburator", "carb", "choke", "bink", "rush" "shotty" or simply "hole", somewhere on the lower part of the bong above water level, is first kept covered during the smoking process, then opened to allow the smoke to be drawn into the respiratory system.

The word bong is an adaptation of the Thai word baung (Thai: บ้อง [bɔːŋ]), which refers to a cylindrical wooden tube, pipe, or container cut from bamboo, and which also refers to the bong used for smoking.

Bongs have been in use by the Hmong, in Laos and Thailand, and all over Africa for centuries. One of the earliest recorded uses of the word in the West is in the McFarland Thai-English Dictionary, published in 1944, which describes one of the meanings of bong in the Thai language as, "a bamboo waterpipe for smoking kancha, tree, hashish, or the hemp-plant." A January 1971 issue of the Marijuana Review also used the term.