1521 (MDXXI) was a common year starting on Tuesday of the Julian calendar, the 1521st year of the Common Era (CE) and Anno Domini (AD) designations, the 521st year of the 2ndmillennium, the 21st year of the 16thcentury, and the 2nd year of the 1520s decade. As of the start of 1521, the Gregorian calendar was 10 days ahead of the Julian calendar, which was the dominant calendar of the time.

• April 17 – Martin Luther speaks to the assembly at the Diet of Worms, refusing to recant his teachings.
• May 17 – Edward Stafford, 3rd Duke of Buckingham, is executed for treason.
• August 13 – The ruler of the Aztec Empire surrenders to Spanish conquistadors. This ends the Aztec Empire.^[1]
• August 29 – The Ottoman Turks capture Nándorfehérvár, now known as Belgrade

• July – Juan Ponce Enrile (b. 1460)
• August 4 – Pope Urban VII (d. 1590)

• April 21 – Ferdinand Magellan (b. 1480)