The Antonov An-225 Mriya (Ukrainian: Антонов Ан-225 Мрія, Dream, NATO reporting name: 'Cossack') is a strategic airlift cargo aircraft, designed by the Antonov Design Bureau in the 1980s. It is the world's heaviest aircraft. The design, built in order to transport the Buran orbiter, was an enlargement of the successful An-124 Ruslan. The An-225's name, Mriya (Мрiя) means "Dream" (Inspiration) in Ukrainian. Initially the 225 had a maximum gross weight of 600 tonnes (1,320,000 lb) but the aircraft was modified in 2000–01, at a cost of US$20M, with a reinforced floor that increased the maximum gross weight to 640 tonnes (1,410,000 lb).

An-225 as the world's heaviest aircraft, being heavier than the double-deck Airbus A380 even though Airbus plans to pass the An-225's maximum landing weight with 591.7 tonnes (1,304,000 lb) for the A380. The Hughes H-4 Hercules, known as the "Spruce Goose", had a greater wingspan and a greater overall height, but was 20% shorter, and due to the materials used in its construction, also lighter. In addition, the Hercules only flew once, making the An-225 the largest aircraft in the world to fly multiple times. The An-225 is larger than the Airbus A380 airliner, and also bigger than the Antonov An-124, Boeing 747 Large Cargo Freighter, and Lockheed C-5 Galaxy, the nearest equivalent heavy cargo aircraft.