Baqubah (Arabic: بَعْقُوبَة; BGN: Ba‘qūbah; also spelled Baquba and Baqouba) is the capital of Iraq's Diyala Governorate. The city is located some 50 km (31 mi) to the northeast of Baghdad, on the Diyala River. In 2003 it had an estimated population of some 280,000 people.

Baqubah served as a way station between Baghdad and Khorasan on the medieval Khorasan Road. During the Abbasid Caliphate, it was known for its date and fruit orchards, irrigated by the Nahrawan Canal. It is now known as the centre of Iraq's commercial orange groves. During the Iraq war, Baqubah served the capital of Al Qaeda in Iraq as well as the Islamic State of Iraq, the predecessors of the Islamic State.

Baqubah's name originates from the Aramaic words "Bet" (house) and "aquba" (Guardian or Punishment) meaning "The house of Punishment/The Guardian's house". The city was used as a refugee camp for Assyrian refugees fleeing the Assyrian genocide. A refugee camp was set up outside the city, which accommodated between 40,000 and 50,000 refugees.

The camp set up by the British mandate government in Iraq housed Assyrians and Armenians following the 1915 Sayfo and Armenian genocide by the Ottoman Empire. The camp was ruled by military authority and the later Assyrians living in the camp were recruited to serve in the Iraq Levies Forces.

Baqubah was probably founded during the Sasanian period.

At the time of the Abbasid caliphate, Baqubah lay on the Nahrawan canal, at the end of the canal's Great Qātūl stage and the beginning of its Tāmarrā stage. Although the main road heading east to Khorasan from Baghdad bypassed Baqubah during this period, passing instead through the city of Jisr Nahrawan, it was Baqubah and not Jisr Nahrawan that was the capital of the Upper Nahrawan district.

However, the succeeding Seljuk sultans neglected to dredge the Nahrawan canal or otherwise maintain it, and by the time of Yaqut al-Hamawi in the early 1200s, the canal had completely silted up and the lands it had once watered had gone out of cultivation. By the 14th century, Hamdallah Mustawfi wrote that Jisr Nahrawan was in ruins, and the road to Khorasan now passed through Baqubah instead. Baqubah was the main town in the Tarīq-i-Khurāsān district, and it was surrounded by fertile orchards that produced large crops of oranges and pomelos.

In Yaqut's time, Baqubah was a flourishing town, with several public baths and mosques, as well as a market. The land around Baqubah was densely covered in irrigated orchards, whose dates and lemons were proverbial for their excellence.