A curb (American English) or kerb (British English) is the edge where a raised sidewalk/pavement or road median/central reservation meets a street/other roadway.

Although curbs have been used throughout modern history, and indeed were present in ancient Pompeii, their widespread construction and use only began in the 18th century, as a part of the various movements towards city beautification that were attempted in the period.

A series of Paving Acts in the 18th century, especially the 1766 Paving and Lighting Act, authorized the City of London Corporation to create footways along the streets of London, pave them with Purbeck stone (the thoroughfare in the middle was generally cobblestone) and raise them above street level with curbs forming the separation. The corporation was also made responsible for the regular upkeep of the roads, including their cleaning and repair, for which they charged a tax from 1766.

Previously, small wooden bollards had been put up to demarcate the area of the street reserved for pedestrian use. By the late 18th century, this method of separating pedestrians from carriageways had largely been supplanted by the use of curbs. With the introduction of macadam roads in the early 19th-century, curbs became ubiquitous in the streets of London.

Curbs present an obstacle for accessibility to physically disabled persons in public spaces. In 1945, Jack Fisher of Kalamazoo, Michigan, celebrated the installation of one of the nation's first curb cuts to facilitate mobility in the center of the city. In the United States, activism and passage of federal legislation on accessibility requirements such as the Americans with Disabilities Act of 1990 (ADA) have facilitated travel for wheelchair users and other people.

Curbs may fulfill any or several of a number of functions. By delineating the edge of the pavement, they separate the road from the roadside and discourage drivers from parking or driving on sidewalks and lawns. They also provide structural support to the pavement edge. Curbs can be used to channel runoff water from rain or melted snow and ice into storm drains.

There is also an aesthetic aspect, in that curbs look formal and "finished".^{[citation needed]}

Since curbs add to the cost of a road, they are generally limited to urban and suburban areas and are rarely found in rural areas except where certain drainage conditions (such as mountains or culverts) make them necessary. Curbs are not universally used, however, even in urban settings (see living street).