乔姆斯基体系是刻画形式文法表达能力的一个分类谱系，是由诺姆·乔姆斯基于1956年提出的。它包括四个层次：

正规语言类包含于上下文无关语言类，上下文无关语言类包含于上下文相关语言类，上下文相关语言类包含于递归可枚举语言类。这里的包含都是集合的真包含关系，也就是说：存在递归可枚举语言不属于上下文相关语言类，存在上下文相关语言不属于上下文无关语言类，存在上下文无关语言不属于正规语言类。

下表总结了上述四种类型的文法的主要特点：

A -> a

Within the fields of computer science and linguistics, specifically in the area of formal languages, the Chomsky hierarchy (occasionally referred to as Chomsky-Schützenberger hierarchy) is a containment hierarchy of classes of formal grammars. This hierarchy of grammars was described by Noam Chomsky in 1956. It is also named after Marcel-Paul Schützenberger, who played a crucial role in the development of the theory of formal languages.