Drunk driving is the act of operating and/or driving a motor vehicle while under the influence of alcohol and/or drugs to the degree that mental and motor skills are impaired. It is illegal in all jurisdictions within the U.S. The specific criminal offense is usually called driving under the influence [of alcohol and/or other drugs] (DUI), and in some states driving while intoxicated (DWI), operating while impaired (OWI), or operating a vehicle under the influence (OVI). Such laws may also apply to boating or piloting aircraft. Vehicles can include farm machinery and horse-drawn carriages.

With alcohol, a drunk driver’s level of intoxication is typically determined by a measurement of blood alcohol content or BAC. A BAC measurement in excess of a specific threshold level, such as 0.05% or 0.08%, defines the criminal offense with no need to prove impairment. In some jurisdictions, there is an aggravated category of the offense at a higher BAC level, such as 0.12%.