Year 911 (CMXI) was a common year starting on Tuesday (link will display the full calendar) of the Julian calendar.
- September 24 — King Louis IV (the Child), the last ruler of the Carolingian Dynasty, dies at Frankfurt am Main after an 11-year reign. The East Frankish dukes elect Conrad I at Forchheim as the king of the East Frankish Kingdom. Charles III is elected as king of Lotharingia. Conrad is chosen through the influence of Louis' guardian and regent, Hatto I, archbishop of Mainz.
- Autumn – King Charles III (the Simple) and Rollo, leader of the Vikings, sign a peace agreement (Treaty of Saint-Clair-sur-Epte). In return for his homage and conversion to Christianity, Rollo becomes a vassal and is made Count of Rouen. He divides the lands between the riviers Epte and Risle among his chieftains, and prevents any other Vikings sailing down the Seine to attack the West Frankish Kingdom.
- The Hungarians cross Bavaria, and invade Swabia and Franconia. They plunder the territories from Minfeld to Aargau. After that, they cross the Rhine, and attack Burgundy for the first time.
- The Fatimids begin the conquest of Sicily, over their Aghlabid archrivals. Fatimid Sicilian governor Ibn al-Khinzir raids the south Italian coast (approximate date).
- February 28 – Abu Abdallah al-Shi'i, Muslim Shia imam
- April 4 – Liu Yin, governor of Southern Han (b. 874)
- April 14 – Sergius III, pope of the Catholic Church
- August 19 – Al-Hadi ila'l-Haqq Yahya, Arab religious leader (b. 859)
- Æthelred, lord of Mercia and husband of Æthelflæd
- Burchard I, Frankish nobleman
- Ibn al-Rawandi, Muslim scholar and writer (b. 827)
- Louis IV, king of the East Frankish Kingdom (b. 893)
- Lu Yanchang, Chinese governor (jiedushi)
- Tecpancaltzin Iztaccaltzin, ruler of the Toltec Empire
- Wifred II, count of Barcelona
- ^ John Haywood (1995). Historical Atlas of the Vikings, p. 80. Penguin Books: ISBN 978-0-140-51328-8.
- ^ Meynier, Gilbert (2010). L'Algérie, cœur du Maghreb classique: De l'ouverture islamo-arabe au repli (658-1518). Paris: La Découverte. p. 38.