Qasr al-Azraq (Arabic: قصر الأزرق, "Blue Fortress") is a large fortress located in present-day eastern Jordan. It is one of the desert castles, located on the outskirts of present-day Azraq, roughly 100 km (62 mi) east of Amman.

Its strategic value came from the nearby oasis, the only water source in a vast desert region. The name of the fortress and associated town came from these. The settlement was known in antiquity as Basie and the Romans were the first to make military use of the site, and later an early mosque was built in the middle. It did not assume its present form until an extensive renovation and expansion by the Ayyubids in the 13th century, using locally quarried basalt which makes the castle darker than most other buildings in the area.

Later, it would be used by the Ottoman armies during that empire's hegemony over the region. During the Arab Revolt, T. E. Lawrence based his operations here in 1917–18, an experience he wrote about in his book Seven Pillars of Wisdom. The connection to "Lawrence of Arabia" has been one of the castle's major draws for tourists.