|Centuries:||7th century – 8th century – 9th century|
|Decades:||750s 760s 770s – 780s – 790s 800s 810s|
|Years:||786 787 788 – 789 – 790 791 792|
|789 by topic|
|State leaders – Sovereign states|
|Birth and death categories|
|Births – Deaths|
|Establishment and disestablishment categories|
|Establishments – Disestablishments|
|Ab urbe condita||1542|
|Bahá'í calendar||−1055 – −1054|
|English Regnal year||N/A|
|Chinese calendar||戊辰年 (Earth Dragon)
3485 or 3425
— to —
己巳年 (Earth Snake)
3486 or 3426
|- Vikram Samvat||845–846|
|- Shaka Samvat||711–712|
|- Kali Yuga||3890–3891|
|Igbo calendar||−211 – −210|
|Japanese calendar||Enryaku 8
|Minguo calendar||1123 before ROC
|Thai solar calendar||1332|
|Wikimedia Commons has media related to 789.|
Year 789 (DCCLXXXIX) was a common year starting on Thursday (link will display the full calendar) of the Julian calendar. The denomination 789 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.
- King Charlemagne crosses the Elbe River with a Frankish-Saxon army into Obotrite territory. He submits the Wiltzes and reaches the Baltic.
- King Pepin of Italy conquers Istria on the Adriatic, ignoring Byzantine protests. He establishes a tributary march and sends missionaries.
- Charlemagne issues the Admonitio generalis, which covers educational and ecclesiastical reforms within the Frankish Kingdom. 
- Charlemagne founds the town of Herford (modern Germany) in order to guard a ford crossing the narrow Werre River.
- King Beorhtric of Wessex marries princess Eadburh, daughter of king Offa of Mercia, and accepts Mercian overlordship.
- Constantine I is installed as king of the Picts. He becomes one of the greatest Scottish monarchs in the Viking period.
- The Anglo-Saxon Chronicle records the first appearance of Vikings in England (see 787).
- Al-Khayzuran, widow of former Abbasid caliph Al-Mahdi, dies, leaving more of the effective power in the hands of Harun al-Rashid.
- The city of Fes (modern Morocco) is founded by emir Idris I, founder of the Zaydi Shi'te Idrisid dynasty.
- An uprising in Japan leads to a major defeat for emperor Kanmu, alongside a severe drought and famine—the streets of the capital Nagaoka-kyō are clogged with the sick.
- Al-Khayzuran, wife of Al-Mahdi
- Hildeprand, duke of Spoleto
- Mauregatus, king of Asturias (or 788)
- Torson, Frankish count of Toulouse (or 790)
- November 8 – Willehad, bishop of Bremen
- Jeep (2001), pp. 5–6