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Year 1455 (MCDLV) was a common year starting on Wednesday (link will display the full calendar) of the Julian calendar.
- January 8 – Pope Nicholas V publishes Romanus Pontifex, an encyclical addressed to King Afonso V of Portugal, which sanctions the conquest of non-Christian lands, and the reduction of native non-Christian populations to 'perpetual slavery' (later there will be a dramatic reversal when, in 1537, the bull Sublimis Deus of Pope Paul III forbids the enslavement of non-Christians).
- February 23 – The Gutenberg Bible is the first book printed with movable type.
- April 8 – Pope Calixtus III succeeds Pope Nicholas V, as the 209th pope.
- Spring – The Wars of the Roses begin in England.
- May 1 – Battle of Arkinholm: Forces loyal to King James II of Scotland defeat the supporters of the Earl of Douglas.
- May 22 – First Battle of St Albans: Richard, Duke of York, defeats and captures King Henry VI of England.
- November 15 – The conflict between Vladislav II of Wallachia and John Hunyadi escalates, so the latter decides to support Vlad the Impaler for the throne of Wallachia, the following year.
- January 9 – William IV, Duke of Jülich-Berg, Count of Ravensberg (d. 1511)
- January 29 – Johann Reuchlin, German-born humanist and scholar (d. 1522)
- February 2 – King John of Denmark, Norway, and Sweden (d. 1513)
- March 3
- March 15 – Pietro Accolti, Italian Catholic cardinal (d. 1532)
- May 16 – Wolfgang I of Oettingen, German count (d. 1522)
- June 1 – Anne of Savoy, Savoy royal (d. 1480)
- July 9 – Frederick IV of Baden, Dutch bishop (d. 1517)
- July 15 – Queen Yun, Korean queen (d. 1482)
- August 2 – John Cicero, Elector of Brandenburg (d. 1499)
- August 15 – George, Duke of Bavaria (d. 1503)
- November 9 – Johann V of Nassau-Vianden-Dietz, Lord of Breda and Stadtholder of Guelders and Zutphen (d. 1516)
- date unknown