郊区（亦称邻近都市区域、市郊）是指城市外围人口较多的区域。通常是商业区较少，而以住宅为主，或者还有相当程度农业活动但属于都市行政辖区的地区。因此在都市圈和先进国家，有许多人口居住郊区但就业和日常活动空间主要在城市里。

通常一个在城市的周边、有一定程度的人口之自治区域，要被认定为是「郊区」的条件必须：具备商业、行政的基本服务、是连续区域（郊区的详细定义，不同的都市计划师有不同见解）。人口密度普通，但比都市中心周边的住宅密集区域（内都市）要来得低（若因为政府或财团的计划性开发，兴建大规模的住宅，这时郊区的人口密度就会提高）。

A suburb is a residential area or a mixed use area, either existing as part of a city or urban area or as a separate residential community within commuting distance of a city. In most English-speaking regions, suburban areas are defined in contrast to central or inner city areas, but in Australian English, "suburb" has become largely synonymous with what is called a "neighborhood" in other countries and the term extends to inner city areas. In some areas, such as Australia, China, New Zealand, the United Kingdom, and a few U.S. states, new suburbs are routinely annexed by adjacent cities. In others, such as Arabia, Canada, France, and much of the United States, many suburbs remain separate municipalities or are governed as part of a larger local government area such as a county.