A cage is a closure, usually made of a net, bar, or line, used to limit, contain, or protect something or something. Cages can be used for many purposes, including keeping animals in captivity, capturing and displaying animals in zoos.

One of the most important characteristics of cages is that they can't keep objects airtight and isolated from the external environment. Compared with baskets, cages are usually closed on all sides. When used as a transport container, a metal crate constructed as an open crate can be called a cage.