在计算机科学中，联合体（英语：union）又名共用体，是一种具有多个类型或格式的值，或者把它定义为一种由具有这样的值的变量形成的数据结构。一些编程语言可以支持被称为“联合体”的特殊的数据类型，来表示上述的变量。换句话说，一个联合体的定义（defenition）会指定一些允许的可以存储在实例内的原始数据类型（例如整型，浮点）。和记录(record)（或结构，structure）那些可以被定义去包含一个浮点数或整型不同的是，在一个联合体任何时候只有一个值。

在C语言中，一个典型的例子如下：

In computer science, a union is a value that may have any of several representations or formats; or it is a data structure that consists of a variable that may hold such a value. Some programming languages support special data types, called union types, to describe such values and variables. In other words, a union type definition will specify which of a number of permitted primitive types may be stored in its instances, e.g., "float or long integer". Contrast with a record (or structure), which could be defined to contain a float and an integer; in a union, there is only one value at any given time.