The Bashmurian revolts (Coptic: Ⲡⲓⲧⲱⲟⲩⲛ Ⲙ̀ⲡⲓϣⲁⲙⲏⲣ; Egyptian Arabic: ثورة البشموريين) were a series of revolts by the Egyptian Copts in the Bashmur region in the north of the Nile Delta against the Umayyad Caliphate and Abbasid Caliphate in the eighth and ninth centuries. Exactly how many revolts took place cannot be determined, but the major military conflicts took place in 749, 767 and 831–832.

The Bashmurian revolts are known from Coptic and Arabic sources. They did not become known in Europe until the early nineteenth century.

The early years of Arab rule over the Copts were marked by relative peace but eventually gave way to significant subjugation and economic oppression. Both Coptic and Arabic sources attribute them to oppressive taxation and the unjust treatment of Christians by some Umayyad and Abbasid governors.

This was particularly evident during the reign of the caliph al-Walid I, under which the Copts faced harsher restrictions on their language and religious practices, and particularly with the enactment of a regressive poll tax and threats of the destruction of their churches. The Bashmurian revolts aimed to overthrow Arab rule and liberate Egypt from foreign oppression. While initially successful, these revolts ended disastrously for the Copts. The suppression of the Bashmurian revolts not only crushed the resistance, but destroyed Bashmur and resulted in many Copts sold into slavery, which made future organized rebellions impossible.

The exact boundaries of Bashmur varied over time depending on where the Bashmurians were settled. At the time of the revolts, it seems to have lain across the northern Delta just south of the Mediterranean from Fuwwa in the west to Ashmun al-Rumman in the east. By the thirteenth century, the Bashmurians seem to have been confined to the eastern Delta. In the eighth century, they were perhaps concentrated in the west, around the lake of Edku.

Bashmur was a region of marshland with sand banks and dense cover of reeds. Nowhere else in Egypt was more propitious for armed rebellion. Access to inhabited places was provided through narrow sandy banks and the reeds provided cover for soldiers. Moreover, Arabs did not settle in the Bashmur, leaving the population religiously unmixed. The economy of the region also favoured the Bashmurians, who relied on limited agriculture, fishing and hunting birds for food. Less dependent on irrigation works than the fellahin, they were capable of resisting long sieges. The Bashmurians also sold papyrus and possibly raised cattle.

The rebels and inhabitants of Bashmur were also known in the Arabic sources under the name Biyama (بيَمة), which Eutychius derives from Coptic ⲡⲁϩⲙⲉ lit. 'the offspring of forty', relating to a story that when the Byzantines withdrew from the Delta, only forty men remained behind in Bashmur, and that they were the ancestors of the Biyama. This etymology is more legendary than historical, as al-Maqrīzī states that all Copts living in Lower Egypt are called Biyama. It is rather to be derived from a Coptic word for "cattle herdsman" (Coptic: ⲡⲓⲁⲙⲏ, romanized: piamē), a Greek translation of which is βουκόλος "herdsman", another name for the Bashmurian rebels and the inhabitants of the marshy eastern shore of the Lake Burullus called Boucolia (Ancient Greek: τὰ Βουκόλια), who also revolted against the Roman rule under the lead of Isidorus in the 2nd century.

It is impossible to say when the first Bashmurian revolt in the region broke out. Although there had been Coptic revolts in Egypt as early as the seventh century, most were quickly crushed. Only the Bashmurians were able to resist for long periods, inflict heavy losses on the government and endure long sieges. Of the nine recorded Egyptian revolts between 693/694 and 832, only the Bashmurian revolts required the personal intervention of the caliphs.