As with most questions aimed at identifying what the most or least is in a given category, the question of what's the fastest airplane has a nuanced answer. To make answering the question still more complex, available information on the fastest airplane is not abundant as governments and their agencies, such as NASA (the National Aeronautics and Space Administration), keep this information somewhat confidential.

With that caveat, we can still attempt an answer. If having a pilot on board is not a criteria, then the X-43 is said to be the fastest airplane in the world. The X-43 is an unmanned scramjet which launches not from the ground but from a B-52 at about 40,000 feet (12.2 kilometers) in the air. On November 16, 2004 the X-43 reached Mach 9.6 (7,000 miles or 11,265 kilometers per hour) according to NASA. Some claim that it reached Mach 9.8.

If the type of engine is not limited to say, jet powered engines, then the North American X-15 is the fastest airplane in the world. Powered by a rocket engine, the X-15 is said to have reached speeds of Mach 6.85, or 4,520 miles per hour (7,274 kilometers per hour). Like the X-43, it too is launched mid-air from a B-52. The X-15 has also achieved altitude records by reaching 67 miles (107.8 kilometers) on August 22, 1963, earning some of its pilots the designation of "astronaut" by the United States Air Force (USAF). Because the X-15 is powered by a rocket engine however, it is technically half rocket, arguably eliminating it from the running of fastest airplane in the world.

When discussing the world's fastest airplane, Lockheed's SR-71 often comes up. Also referred to as the Blackbird, the SR-71 made its maiden flight on December 22, 1964. It's a jet powered and piloted airplane which is said to have reached Mach 3.2 (2,094 miles or 3,370 kilometers per hour) making it the fastest airplane in the world. Some speculate, that its true top speed and other capabilities were never revealed. The SR-71 is said to have reached an altitude of 16.1 miles (25.9 kilometers).

The fastest airplane commercially was the Tupolev Tu-144, nicknamed the Concordski or Konkordski, which is said to have reached Mach 2.35 (1,550 miles or 2,494.4 kilometers per hour). Because of technical and safety problems however, the Russian company retired the Tu-144 after a short time, but is said to be working on a replacement. Currently the fastest commercial airliner in operation is the Concorde which generally flies at Mach 2.02 (1,330 miles or 2,140.4 kilometers per hour). To compare, the Boeing 747 operates at a cruising speed of about 550 miles per hour (885.1 kilometers per hour).