1171 (MCLXXI) was a common year starting on Friday of the Julian calendar, the 1171st year of the Common Era (CE) and Anno Domini (AD) designations, the 171st year of the 2nd millennium, the 71st year of the 12th century, and the 2nd year of the 1170s decade. As of the start of 1171, the Gregorian calendar was 7 days ahead of the Julian calendar, which was the dominant calendar of the time.

• Saladin bans the Fatimid Caliphate, bringing back Sunni rule in Egypt.
• Manuel I Comnenus orders all the Venetians in the Byzantine Empire to be arrested.
• Rhys ap Gruffydd agrees to talk to Henry II of England.
• Building of the Cathedral of Saint Sabino in Bari is finished.
• Serbian ruler Stefan Nemanja begins to rule alone.
• Alfonso II of Aragon beats Caspe and Teruel.
• Henry II of England starts eight centuries of conflict and war between Ireland and England.
• Pisa and Florence make an alliance against Lucca and Genoa.
• The Heirs of Robert Burdet leave Catalonia.

• August 15 — King Alfonso IX of León (d. 1230)
• Agnes of France, daughter of Louis VII of France (d. after 1207)

• January 1 — Diarmait Mac Murchada, King of Leinster (b. 1110)
• February 20 — Conan IV, Duke of Brittany (b. 1138)
• November 8 — Baldwin IV, Count of Hainaut (b. 1108)
• Henry of Blois, bishop of Winchester (b. 1111)
• Gleb of Kiev