A central business district (CBD) is the commercial and business center of a city. It contains commercial space and offices, and in larger cities will often be described as a financial district. Geographically, it often coincides with the "city center" or "downtown". However, these concepts are not necessarily synonymous: many cities have a central business district located away from its commercial and or cultural center and or downtown/city center, and there may be multiple CBDs within a single urban area. The CBD will often be characterised by a high degree of accessibility as well as a large variety and concentration of specialised goods and services compared to other parts of the city. For instance, Midtown Manhattan, New York City, is the largest central business district in the city and the world. London's city center is usually regarded as encompassing the historic City of London and the medieval City of Westminster, while the City of London and the transformed Docklands area containing Canary Wharf are regarded as their two respective CBDs. In Chicago, the Chicago Loop is the second-largest central business district in the United States. It is also referred to as the core of the city's downtown. Mexico City also has its own historic city center, the colonial-era "Centro Histórico," along with two CBDs: the mid-late 20th century Paseo de la Reforma – Polanco, and the new Santa Fe, respectively. Moscow and Russia's largest central business district is the Moscow International Business Center.

The shape and type of a CBD almost always closely reflect the city's history. Cities with strong preservation laws and maximum building height restrictions to retain the character of the historic and cultural core will have a CBD quite a distance from the city center. This practice is quite common for European cities such as Paris, Moscow, Vienna, Prague or Budapest. In cities in the New World that grew quickly after the invention of modern transportation such as road or rail, a single central area or downtown will often contain most of the region's tallest buildings and act both as the CBD and the commercial and cultural city center. Increasing urbanization in the 21st century have developed megacities, particularly in Asia, that will often have multiple CBDs scattered across the urban area. It has been said that downtowns (as understood in North America) are therefore conceptually distinct from both CBDs and city centers. Although no two CBDs look alike in terms of their spatial shape, however, certain geometric patterns in these areas are recurring throughout many cities due to the nature of a centralized commercial and industrial activities.