Mumbai City District (मुंबई जिल्हा) is a district of Maharashtra in Konkan Division. As a city district, it has no headquarters or subdivisions. It, along with the Mumbai Suburban District make up the metropolis of Mumbai. The city area is called the "island city" or South Mumbai or Old Mumbai. It extends from Colaba in the south to Mahim and Sion in the north. Until the 1960s, the area was known as Mumbai. Today, Mumbai municipality includes both districts. The city's area covers 67.7 km².

The City of Bombay, as it was then called came in light in the year 150 A.D. through the geographical work of renowned geographer, Ptolemy. The City consisting of several islands were then ruled by Marathi kolis and agris, the native inhabitants of Mumbai.

These natives ruled the islands up to 1345 A.D. Thereafter, the rulers changed down the history till the Islamic rulers invaded India and conquered some of the islands in 1534 A.D. Subsequently, a Muslim ruler from Gujarat took over all the islands, which were then conquered by the Portuguese. In 1661 A.D., the island of Bombay was added to the Britishers as a part of Royal Dowry, on the occasion of the marriage of King Charles II of England with the Portuguese princess Infanta Catherine.

Mumbai /mʊmˈbaɪ/, also known as Bombay /bɒmˈbeɪ/, is the capital of the Indian state of Maharashtra. It is the most populous city in India, and the fourth most populous city in the world, with a total metropolitan area population of approximately 20.5 million. Along with the neighbouring urban areas, including the cities of Navi Mumbai and Thane, it is one of the most populous urban regions in the world. Mumbai lies on the west coast of India and has a deep natural harbour. In 2009, Mumbai was named an Alpha world city. Mumbai is also the richest city in India, and has the highest GDP of any city in South, West or Central Asia.

The seven islands that came to constitute Mumbai were home to communities of fishing colonies. For centuries, the islands were under the control of successive indigenous empires before being ceded to the Portuguese and subsequently to the British East India Company. During the mid-18th century, Mumbai was reshaped by the Hornby Vellard project, which undertook the reclamation of the area between the seven constituent islands from the sea. Completed by 1845, the project along with construction of major roads and railways transformed Bombay into a major seaport on the Arabian Sea. Economic and educational development characterised the city during the 19th century. It became a strong base for the Indian independence movement during the early 20th century. When India became independent in 1947, the city was incorporated into Bombay State. In 1960, following the Samyukta Maharashtra movement, a new state of Maharashtra was created with Bombay as capital. The city was renamed Mumbai in 1996.

City district is a type of administrative division of Pakistan and Croatia.

It is also the English translation of German Stadtbezirk and Swedish Stadsdel.