城市蔓延或都市蔓延是指都市大幅向外发展，侵占都市边缘的乡郊地区。

都市蔓延地区的人口密度较低，住宅多属低密度住宅。在交通上，相当依赖小汽车。

不良后果：

• 交通挤塞（因居民以小汽车出入为主）。
• 自然景观受破坏。
• 改变农地用途。
• 郊区水质受污染，影响渔农业，危害动植物健康。

Urban sprawl or suburban sprawl describes the expansion of human populations away from central urban areas into low-density, monofunctional and usually car-dependent communities, in a process called suburbanization. In addition to describing a particular form of urbanization, the term also relates to the social and environmental consequences associated with this development. In Continental Europe the term "peri-urbanisation" is often used to denote similar dynamics and phenomena, although the term urban sprawl is currently being used by the European Environment Agency. There is widespread disagreement about what constitutes sprawl and how to quantify it. For example, some commentators measure sprawl only with the average number of residential units per acre in a given area. But others associate it with decentralization (spread of population without a well-defined centre), discontinuity (leapfrog development, as defined below), segregation of uses, and so forth.