The aircraft with the highest standard maximum take-off weight is the Antonov An-225 "Mriya" (Dream) at 600 tonnes (1.32 million lb). A heavy-lift version of the standard Antonov An-124 "Ruslan" cargo plane, only two of these behemoths were ever built.
It was built in the Ukraine (when part of the USSR) to carry the former Soviet space shuttle Buran. It has a wing span of 88.4 m (290 ft) - the greatest of any aircraft currently flying. The An-225 first flew on 21 December 1988.
For comparison, the maximum takeoff weight of a Boeing 747-400 (Jumbo) is 396.89 tonnes (875,000 lb).
No more than two (some sources say one) of these giants was ever built, and it is uncertain whether any remain in service (March 2001).
Comments below may relate to previous holders of this record.