The Casbah (French) or more correctly Qasbah (from Arabic qasbah, قصبة, 'citadel') is specifically the citadel of Algiers and the traditional quarter clustered round it. More generally, kasbah denotes the walled citadel of many North African cities and towns. The word made its way into English from French in the late 19th century (the O.E.D. says 1895), hence its conventional English spelling.

In Rabat, since 1912 the capital of Morocco, the Casbah of the Oudaya is the military barracks encircled by walls with gates, built in the 16th and 17th centuries on ancient foundations.

In the 1938 movie Algiers, (a remake of a French film of the previous year), Charles Boyer, as the master criminal Pepe le Moko, holed up in the narrow alleyways of the Casbah and pursued by the relentless French inspector, who waits for his first false move, falls for lovely American tourist Gaby (Hedy Lamarr, in her first Hollywood film). Though Charles Boyer never actually says "Come with me to the casbah", this was most Americans' introduction to the picturesque alleys and souks of the Casbah. In 1948 a musical remake, Casbah, was released.

In 1982 the British London based punk rock group The Clash released the single "Rock The Casbah" which reached position #30 in the UK music charts. The following year the single was released in the US reaching #8 in the charts. "Rock The Casbah" was also the first song played on the Armed Forces Radio during Operation Desert Shield. It has become an unofficial anthem for the Armed Forces during the Gulf War conflicts.