Year 1215 (MCCXV) was a common year starting on Thursday (link will display the full calendar) of the Julian calendar.
March 4 – King John of England makes an oath to Pope Innocent III as a crusader to gain his support.
June 1 – Mongol conquest of the Jin dynasty: after the long Battle of Zhongdu, Genghis Khan's Mongols captured and torched Beijing (the city burns for more than a month).
June 15 – King John of England is forced by rebellious barons of England at Runnymede to put the Great Seal of the Realm on a set of articles confirming their rights and those of the towns and Church, and confirming the status of trial by jury, which on June 19 is confirmed as Magna Carta.
August – King John of England rejects Magna Carta, leading to the First Barons' War.
August 24 – Pope Innocent III declares Magna Carta invalid.
November 11 – The Fourth Council of the Lateran gathers in Rome under Pope Innocent III, who adopts the style "Vicar of Christ".
December – First Barons' War: Alexander II of Scotland invades northern England.
Otto IV, Holy Roman Emperor, is excommunicated and forced to abdicate as Emperor and King of Burgundy, replaced by Frederick II (King of the Romans 1212–1250).
The Dominican Order is founded, according to some sources.
Bhiksu Ananda of Kapitanagar completes writing the holy Buddhist book Arya Astasahasrika Prajnaparamita (sutra) in gold ink in Ranjana script.
1215–1216 – The Macy Jug, from Iran, is made. It is now kept at The Metropolitan Museum of Art, New York.
Kalinga Magha from Kalinga Province in India lands in Sri Lanka with a force of 24,000 men, to capture the city of Polonnaruwa and depose its King, Parakrama Pandya.
September 23 – Kublai Khan, 6th Khagan of the Mongol Empire and Genghis Khan's Grandson, founder of the Yuan dynasty (d. February 18, 1294, in Khanbaliq)
Pope Celestine V (d. 1296)
David VII Ulu, King of Georgia (d. 1270)
possiblePope John XXI (d. 1277)
February 3 (or February 4) – Eustace, Bishop of Ely and former Lord Chancellor of England
July 2 – Eisai, Japanese Buddhist priest (b. 1141)
September 1 – Otto, bishop of Utrecht
date unknown – Bertran de Born, French soldier and troubadour