There are a number of ways in which the largest airplane could be determined. Most record-keeping agencies agree that the AN-225 Mriya, an aircraft developed by the Antonov Design Bureau, is the largest airplane in the world. However, a few other craft vie for the title, including the infamous Spruce Goose and the Airbus A380. It's a bit difficult to track down an AN-225, since the aircraft has not been mass-produced and it is only used for specialty cargo, but the plane is still in active use, so most authorities consider giving it credit as the largest aircraft in the world.
The maximum takeoff weight of the AN-225 is 1.3 million pounds (600,000 kilograms), and the plane has a wingspan of 290 feet (88 meters). The plane can be configured to carry a variety of cargo, including cargo mounted to the superstructure of the plane, as in the case of space shuttles which have been transported by the AN-225. As of 2008, only one AN-225 was in operation, although there were plans to refurbish a second aircraft.
In terms of wingspan, however, the AN-225 is overshadowed by the Spruce Goose, formally known as the Hughes H-4 Hercules, which measures 319 feet (97 meters). The Hughes H-4 Hercules is also the tallest recorded airplane, as 79 feet (24 meters) in height, and it holds the records for the largest airplane made of wood, and the largest flying boat. The maximum takeoff weight for this aircraft is significantly less than that of the AN-225, with the Spruce Goose topping out at 400,000 pounds (180,000 kilograms).
The Airbus A380, rolled out in 2005 by the Airbus company, is the largest airplane for passengers. It can carry 550 passengers, 50 more than the Boeing 747, and it has a maximum takeoff weight of 1.23 million pounds (560,000 kilograms). By contrast, the Boeing 747 can take off with only 900,000 pounds (405,000 kilograms), and up to 500 passengers, depending on how the plane is configured. The 747 did dominate the passenger trade for 30 years, and it was nicknamed the “Jumbo Jet” because of its formidable size and fame.
Militaries around the world also use very large aircraft for transport of troops, cargo, and equipment. The Lockheed C-5 Galaxy transport plane operated by the United States is the largest airplane for military use, with a wingspan of 222 feet (67 meters) and a maximum takeoff weight of 840,000 pounds (381,000 kilograms).