Year 1089 (MLXXXIX) was a common year starting on Monday of the Julian calendar.

• April 20 (possible date) – Demetrius Zvonimir, king of Croatia, dies after a 12-year reign, and is succeeded by Stephen II. Zvonimir's widow, Helena of Hungary, Queen of Croatia, plots the inheritance of the Croatian crown for her brother, King Ladislaus I of Hungary.
• June 24 – Reconquista: Gaston IV, Viscount of Béarn (supported by French crusaders) reconquers the Aragonese city of Monzón from Emir Al-Mustain II of the Taifa of Zaragoza.^[1]
• August 18 – Henry IV, Holy Roman Emperor, marries Eupraxia of Kiev (daughter of Grand Prince Vsevolod I) at Cologne. She is crowned and assumes the name Adelaide (or Adelheid).
• King George II abdicates the throne in favour of his 16-year-old son David IV ("the Builder") who becomes ruler of Georgia (until 1125).

• August 11 – A powerful earthquake is recorded in England.
• Northumbria is divided by King William II into the counties of Northumberland, County Palatine of Durham, Yorkshire, Westmorland and Lancashire.^{[citation needed]}

• March 21 – Cîteaux Abbey, the first Cistercian monastery, is established by a group of French monks under Robert of Molesme in southern France.
• August 28 – Braga Cathedral in the County of Portugal has its reconstruction (following 353 years of Muslim occupation) completed sufficiently for its consecration to the Virgin Mary to take place.
• September
  • The Synod of Melfi, led by Pope Urban II (his first papal council), issues decrees against simony and clerical marriage.^[2]
  • A church council, held in Constantinople, discuses relations between Eastern and Western Christianity.^[3]

• Abraham ibn Ezra, Jewish rabbi and philosopher (d. 1167) (approximate date)
• Berthold of Zwiefalten, German abbot and writer (d. 1169) (approximate date)
• Dahui Zonggao, Chinese Zen Buddhist monk (d. 1163)
• Han Shizhong, Chinese general of the Northern Song dynasty (d. 1151)
• Mahsati, Persian female poet and writer (approximate date)
• Richard de Luci, Norman High Sheriff of Essex (d. 1179)
• Sigurd the Crusader, king of Norway (d. 1130)
• Wulgrin II, count of Angoulême (approximate date)

• April 20 (possible date) – Demetrius Zvonimir, king of Croatia and Dalmatia
• May 24 – Lanfranc, Italian-born archbishop of Canterbury
• May 29/30 – Mah-i Mulk Khatun wife of caliph al-Muqtadi (r. 1075–1094).
• May 31 – Sigwin von Are, archbishop of Cologne
• October 6 – Adalbero, Prince-Bishop of Würzburg
• November 11 – Peter Igneus, Italian cardinal-bishop
• December 22 – William the Walloon, French abbot
• Agnes of Aquitaine, French-born countess consort of Savoy
• Donnchad mac Domnaill Remair, Irish king of Dublin, killed (approximate date)
• Durandus of Troarn, French monk and theologian
• Isaac ibn Ghiyyat, Spanish Jewish rabbi and philosopher
• Mieszko Bolesławowic, Polish prince of Kraków
• Renauld II, French count of Nevers and Auxerre
• Theobald III, Count of Blois (or Thibaut), French nobleman