1204 (MCCIV) was a leap year starting on Thursday of the Julian calendar, the 1204th year of the Common Era (CE) and Anno Domini (AD) designations, the 204th year of the 2nd millennium, the 4th year of the 13th century, and the 5th year of the 1200s decade.
|Centuries:||12th century – 13th century – 14th century|
|Decades:||1170s 1180s 1190s – 1200s – 1210s 1220s 1230s|
|Years:||1201 1202 1203 – 1204 – 1205 1206 1207|
|Ab urbe condita||1957|
|Balinese saka calendar||1125–1126|
|English Regnal year||5 Joh. 1 – 6 Joh. 1|
|Chinese calendar||癸亥年 (Water Pig)|
3900 or 3840
— to —
甲子年 (Wood Rat)
3901 or 3841
|- Vikram Samvat||1260–1261|
|- Shaka Samvat||1125–1126|
|- Kali Yuga||4304–4305|
|Japanese calendar||Kennin 4 / Genkyū 1|
|Minguo calendar||708 before ROC|
|Thai solar calendar||1746–1747|
1330 or 949 or 177
— to —
1331 or 950 or 178
- February – Byzantine emperor Alexius IV is overthrown in a revolution, and Alexius V is proclaimed emperor.
- April 12 – The Fourth Crusade take Constantinople by storm, and pillage the city for three days. End of the Fourth Crusade.
- May 16 – Baldwin, Count of Flanders is crowned emperor of the Latin Empire a week after his election by the members of the Fourth Crusade.
- Theodore I Lascaris flees to Nicaea after the capture of Constantinople, and establishes the Empire of Nicaea; Byzantine successor states are also established in Epirus and Trebizond.
- Boniface of Montferrat, a leader of the Fourth Crusade, founds the Kingdom of Thessalonica.
- The writings of French theologian Amalric of Bena are condemned by the University of Paris and Pope Innocent III.
- Valdemar II, King of Denmark, is recognized as king in Norway.
- Angers and Normandy are recaptured from England by Philip II of France.
- The Cistercian convent of Port-Royal is established.
- The district of Cham becomes subject to Bavaria.
- Philip of Swabia becomes a subject of Hermann I of Thuringia.
- Beaulieu Abbey founded.
- Jersey enjoys self-government thanks to the division of the Duchy of Normandy.
- January 1 – King Haakon III of Norway
- February 8 – Alexius IV Angelus, Byzantine Emperor
- March 31 – Eleanor of Aquitaine, queen of France and England
- August 11 – King Guttorm of Norway
- August 14 – Minamoto no Yoriie, Japanese shogun (born 1182)
- October 21 – Robert de Beaumont, 4th Earl of Leicester
- December 13 – Maimonides, Spanish rabbi and philosopher (born 1135)
- Ban Kulin – ruler of Bosnia (born 1163)
- Amalric of Bena, French theologian
- William de Burgh, English politician
- Emeric of Hungary (born 1174)
- Isaac II Angelus, Byzantine Emperor
- Suleiman II of Rum
- David Soslani, Prince of Ossetia