The First Arab Siege of Constantinople in 674–678 is a major conflict of the Arab–Byzantine Wars, and the first culmination of the Umayyad Caliphate's expansionist strategy towards the Byzantine Empire, led by Caliph Muawiyah I. Muawiyah, who had emerged in 661 as the ruler of the Muslim Arab empire following a civil war, renews aggressive warfare against Byzantium after a lapse of some years and hopes to deliver a lethal blow by capturing the Byzantine capital, Constantinople.As reported by the Byzantine chronicler Theophanes the Confessor, the Arab attack was methodical: in 672–673 Arab fleets secured bases along the coasts of Asia Minor, and then proceeded to install a loose blockade around Constantinople.

They use the peninsula of Cyzicus near the city as a base to spend the winter, and return every spring to launch attacks against the city's fortifications.

Finally, the Byzantines, under Emperor Constantine IV, manage to destroy the Arab navy using a new invention, the liquid incendiary substance known as Greek fire.

The Arab land army in Asia Minor is also defeated by the Byzantines, forcing the Arabs to lift the siege.

The Byzantine victory is of major importance for the survival of the Byzantine state, as the Arab threat recedes for a time.

A peace treaty is signed soon after, and following the outbreak of another Muslim civil war, the Byzantines even experience a period of ascendancy over the Caliphate.The siege leaves several traces in the legends of the nascent Muslim world, although there it is conflated with accounts of another expedition against the city a few years previously, led by the future Caliph Yazid I.

As a result, the veracity of Theophanes's account has been questioned by recent scholars.