The Casbah is the citadel of Algiers in Algeria and the traditional quarter clustered around it. In 1992, the United Nations Educational, Scientific and Cultural Organization (UNESCO) proclaimed Kasbah of Algiers a World Cultural Heritage Site, as "There are the remains of the citadel, old mosques and Ottoman-style palaces as well as the remains of a traditional urban structure associated with a deep-rooted sense of community."

A kasbah, also spelled qasba, qasaba, or casbah, is a fortress, most commonly the citadel or fortified quarter of a city. It is also equivalent to the term alcazaba in Spanish, which is derived from the same Arabic word. By extension, the term can also refer to a medina quarter, particularly in Algeria. In various languages, the Arabic word, or local words borrowed from the Arabic word, can also refer to a settlement, a fort, a watchtower, or a blockhouse.