The Presidential State Car is the official state car used by the President of the United States. Analogous to the President's use of an airplane designated Air Force One, the automobile?traditionally a limousine?is informally known as "Cadillac One".

The President of the United States travels in one of two armoured Cadillac limousine based upon the normal sedan, the Cadillac DTS, with heavy customisation. Lincolns have also been used in the past, most notably by President John F Kennedy.

The current vehicles were custom-built by a company called O'Gara, Hess and Eisenhart, founded in Fairfield, Ohio in 1942, and specializing in armouring limousines for presidents and heads of state. The vehicle's extensive features include dark windows, state-of-the-art communication and protection systems, a hidden desktop for use of the President and the rear of the limousine is fitted with a gas-proof chamber if Cadillac One were to incur a gas attack.[17]

Unlike most other world leaders, with the occasional exception of Queen Elizabeth II, the President's limousines and escort vehicles are transported by the US Air Force for use on all foreign and domestic trips by the Commander-in-Chief. They will then be supplemented by coaches, police vehicles, additional limousines and a fully equipped field ambulance provided by the host nation or state.

A new model is expected to be delivered in time for the inauguration of the next President, Barack Obama in January 2009.