The Citadel of Cairo or Citadel of Saladin (Arabic: قلعة صلاح الدين‎ Qalaʿat Salāḥ ad-Dīn) is a medieval Islamic-era fortification in Cairo, Egypt, built by Salah ad-Din (Saladin) and further developed by subsequent Egyptian rulers. It was the seat of government in Egypt and the residence of its rulers for nearly 700 years from the 13th to the 19th centuries. Its location on a promontory of the Mokattam hills near the center of Cairo commands a strategic position overlooking the city and dominating its skyline. At the time of its construction, it was among the most impressive and ambitious military fortification projects of its time. It is now a preserved historic site, including mosques and museums.

In addition to the initial Ayyubid-era construction begun by Saladin in 1176, the Citadel underwent major development during the Mamluk Sultanate that followed, culminating with the construction projects of Sultan al-Nasir Muhammad in the 14th century. In the first half of the 19th century Muhammad Ali Pasha demolished many of the older buildings and built new palaces and monuments all across the site, giving it much of its present form. In the 20th century it was used as a military garrison by the British occupation and then by the Egyptian army until being opened to the public in 1983. In 1976, it was proclaimed by UNESCO as a part of the World Heritage Site Historic Cairo (Islamic Cairo) which was "the new centre of the Islamic world, reaching its golden age in the 14th century."