|Centuries:||8th century – 9th century – 10th century|
|Decades:||810s 820s 830s – 840s – 850s 860s 870s|
|Years:||839 840 841 – 842 – 843 844 845|
- February 14 – Charles the Bald and Louis the German sign a treaty.
- Oaths of Strasbourg — alliance of Louis the German and Charles the Bald against emperor Lothar — sworn and recorded in vernacular languages.
- Ramiro I succeeds Alfonso II as king of Asturias.
- Uurad is succeeded by Bred, then Ciniod.
- Charles the Bald marries Ermentrude.
- Three year old Michael III succeeds Theophilus (emperor) as emperor of Byzantium.
- End of the reign of caliph Moqtasim.
- Uyghurs leave the Mongolian plateau.