A double-decker bus is a bus that has two storeys or 'decks'. While double-decker long-distance coaches are in widespread use around the world, double-decker city buses are less common. Double-decker buses are popular in some cities of Europe and in parts of Asia, usually in former British colonies (Hong Kong, Singapore etc.) Some double-deckers specialise in short sight-seeing tours for tourists for, as William Ewart Gladstone observed, "the way to see London is from the top of a 'bus". (Gladstone was referring to London's once ubiquitous double-deck horse drawn omnibuses, rather than a motor bus).Elbert Hubbard (1894–1918) The full quote is:
Then he asked if we were going to London. On being told that we were, he spoke for five minutes about the things we should see in the Metropolis. His style was not conversational, but after the manner of a man who was much used to speaking in public or to receiving delegations. The sentences were stately, the voice rather loud and declamatory. His closing words were: "Yes, gentlemen, the way to see London is from the top of a 'bus—from the top of a 'bus, gentlemen."
Cities listed here use double-decker buses as part of their regular mass transit fleet. Cities with only tourist and sightseeing double-decker buses are excluded.