城邦（英语：City-state），又译为城市国家，是指独自拥有主权或行使自治的城市。历史上的城邦通常是大文化圈的一部份，如古希腊城邦（如雅典、斯巴达）、迦南的腓尼基城邦（如推罗、西顿）、中部美洲的玛雅城邦、丝绸之路上的小国（如撒马尔罕、布哈拉）、东非城邦（如基尔瓦、马林迪）和意大利城邦（如佛罗伦萨、威尼斯）。

欧洲历史上有两个重要的城邦时期—古希腊的城邦和文艺复兴时的意大利城邦，现时欧洲的文明都发源自这些时期。然而，这些文明的城邦通常只存活很短时间，因为它们的土地和实力都不足以抵抗周围的外敌。此外，这些小区域组织在松散的地理和文化个体中互存，成为大国创建稳固势力的障碍。故此，他们大多融入于更大的社会体系、以至民族国家。

A city-state is a sovereign state that consists of a city and its dependent territories. Historically, this included famous cities like Rome, Athens, Carthage, and the Italian city-states during the Renaissance—but today only a handful of sovereign city-states exist, with some disagreement as to which are city-states. However, a great deal of consensus exists that the term properly applies to Singapore, Monaco, and Vatican City. In particular, Singapore has been referred to by The Economist as the "world's only fully-functioning city-state".