|1023 by topic|
|Birth and death categories|
|Births – Deaths|
|Establishments and disestablishments categories|
|Establishments – Disestablishments|
|Ab urbe condita||1776|
|Balinese saka calendar||944–945|
|English Regnal year||N/A|
|Chinese calendar||壬戌年 (Water Dog)|
3719 or 3659
— to —
癸亥年 (Water Pig)
3720 or 3660
|- Vikram Samvat||1079–1080|
|- Shaka Samvat||944–945|
|- Kali Yuga||4123–4124|
|Japanese calendar||Jian 3|
|Minguo calendar||889 before ROC|
|Seleucid era||1334/1335 AG|
|Thai solar calendar||1565–1566|
1149 or 768 or −4
— to —
1150 or 769 or −3
Year 1023 (MXXIII) was a common year starting on Tuesday (link will display the full calendar) of the Julian calendar.
- The Judge-Governor of Seville in Al-Andalus (modern Spain) takes advantage of the disintegration of the Caliphate of Córdoba and seizes power as Abbad I, founding the Abbadid dynasty.
- December – Abbad I declares the Taifa of Seville independent from Córdoban rule. Abd ar-Rahman V is proclaimed Caliph at Córdoba.
- April/May (Jian 3, 4th month) – An epidemic in Kyoto (Japan) is so severe that there are corpses in the streets; disease spreads throughout the country.
- 60th birthday and longevity ceremony of Japanese matriarch Minamoto no Rinshi, wife of Fujiwara no Michinaga.
- The Ghaznavid Empire occupies Transoxiana (approximate date).
- The Dom Church at Utrecht (modern Netherlands) is severely damaged by fire. Bishop Adalbold II begins construction of a new Romanesque style church.
- Lý Thánh Tông, Vietnamese emperor (d. 1072)
- Otto I (or Odon), count of Savoy (approximate date)
- Ramon Berenguer I, count of Barcelona (d. 1076)
- William VII ("the Bold"), duke of Aquitaine (d. 1058)
- March 27 – Gebhard I, bishop of Regensburg
- May 28 – Wulfstan (or Lupus), archbishop of York
- October 18 – Zirid princess and regent
- October 21 – Gero, archbishop of Magdeburg
- October 24 – Kou Zhun, Chinese grand chancellor
- November 24 – Eilward, bishop of Dresden-Meissen
- December 5 – Hartwig, archbishop of Salzburg
- Abū Hayyān al-Tawhīdī, Muslim intellectual (b. 923)
- Godfrey II, count and duke of Lower Lorraine (b. 965)
- Llywelyn ap Seisyll, king of Gwynedd and Powys
- Oda of Haldensleben, duchess of the Polans
- Sitt al-Mulk, Fatimid princess and regent (b. 970)