未成年人（未成年者或未成人）是一个社会学或者法学的概念，即是还没有成年的人。法律上，未成年人即是未满法定成年年龄的人，当中包括婴儿、儿童及青少年。

不同的社会或地区对未成年人在心理状态、社会责任、法律责任等有不同于成年人的要求和社会规范，如在社会发达地区，未成年人被视为是上学，每名未成年人必须上学。另一个例子是在世界上不同国家或地区，必须达到当地的成人年龄才可以退学、喝酒、吸烟、投票、买彩票、去赌场、结婚等等。

In law, a minor is a person under a certain age—usually the age of majority—which legally demarcates childhood from adulthood. The age of majority depends upon jurisdiction and application, but is generally 18. Minor may also be used in contexts unconnected to the overall age of majority. For example, the drinking age in the United States is usually 21, and people below this age are sometimes called minors in the context of alcohol law even if they are older than 18. The term underage often refers to those under the age of majority, but may also refer to persons under a certain age limit, such as the drinking age, smoking age, age of consent, marriageable age, driving age, voting age, etc. These age limits are often different from the age of majority.