A beer tap is a valve, or to be more specific, a tap, for controlling the release of beer. A "tap" may be a "faucet", "valve" or "spigot". Beer served from a tap is largely known as draught or draft beer, though beer served from a cask is more commonly called cask ale, while beer from a keg may specifically be called keg beer. There are many different varities of beer taps.

Most bulk beer is supplied in kegs that are served with external pressure. In a normal system, this pressure comes from a cylinder of carbon dioxide, or sometimes nitrogen, which forces the beer out of the keg and up a hose to the bar. At the end of this hose is a valve built into a fixture on the bar. This is a beer tap, and opening it with a small lever causes beer to flow into the glass.

Sometimes, beer kegs that are designed to be connected to the above system are used on their own, mostly at a parties or outdoor events. In this case, a self-contained portable tap is required that allows beer to be served straight from the keg. Because the keg system uses pressure to force the beer up and out of the keg, these taps must have a means of supplying it. The typical "picnic tap" uses a hand pump to push air into the keg; this will cause the beer to spoil faster but is perfectly acceptable if the entire keg will be consumed in a short time. Portable taps with small CO2 cylinders are also available.