公寓（英文 Apartment），为集合式住宅的一种，是城市特有的现象。

在古罗马时代已经有古罗马公寓（insulae）供平民阶级居住。

公寓在华人社会最早出现在上海的弄堂或香港的唐楼。随着城市化，在香港、中国大陆或新加坡等地，在国家政策积极运作下，兴建以公屋、经济适用房及组屋等名称的公寓式集合式住宅。另外，包含上述地区及**的华人地区，今亦有大量私人投资的公寓建筑，这些因素都让公寓于这些地区成为城市居民主要的居住形式。据统计，**百分之七十五的人口居住于以公寓为主的集合式住宅。

在中国大陆称为单元楼或居民楼，香港称为单位，指的是一种生活设施齐备，但只占建筑一部分的居住形态。公寓可能户主自行购买的，或者自业主租入的。

An apartment (in American and Canadian English) or a flat (in British English) is a self-contained housing unit (a type of residential real estate) that occupies only part of a building, correctly, on a single level without a stair. Such a building may be called an apartment building, apartment complex, apartment house (in American English), block of flats, tower block, high-rise or, occasionally mansion block (in British English), especially if it consists of many apartments for rent. In Scotland it is called a block of flats or, if it's a traditional sandstone building, a tenement, which has a pejorative connotation elsewhere. Apartments may be owned by an owner/occupier, by leasehold tenure or rented by tenants (two types of housing tenure).