制服是指一群来自相同团体的人穿着着统一样式的服装，用以辨识其正在做进行的共同事情，或者用来分别其职业或特别身份，例如：学生、警察和军人等。制服也可以制定阶级，例如：在香港，初级护士的制服是粉红色，正式护士的制服是白色等。另外，制服也是生活中角色扮演的道具，表示服从某种规章制度下的人的工作服装，例如：囚犯服装。

有些职业的制服是全世界统一样式，例如民用航空飞机驾驶员的制服，一般为黑色，佩戴飞行标志和肩牌，并且在袖口处缝有代表级别的标志，戴大檐帽及海军制服等等。

有一些地方的学校，例如亚洲的一些国家，都要求学生穿着校服上学。

A uniform is a type of clothing worn by members of an organization while participating in that organization's activity. Modern uniforms are most often worn by armed forces and paramilitary organizations such as police, emergency services, security guards, in some workplaces and schools and by inmates in prisons. In some countries, some other officials also wear uniforms in their duties; such is the case of the Commissioned Corps of the United States Public Health Service or the French prefects. For some public groups, such as police, it is illegal for non members to wear the uniform. Other uniforms are trade dresses (such as the brown uniforms of UPS).