Normal forms are important because they give us a 'standard' way of rewriting and allow us to compare two apparently different grammars G1  and G2. The two grammars can be shown to be equal provided they have the same normal form.

Additionally by rewriting grammars in a standard way we have a structure that can form the input to future stages of a process. For example programs in a high level programming languages have to be converted in more 'basic' instructions via a parser  and it is helpful if the inputs to such a process are of a uniform type.

In this section we introduce one of the standard normal forms commonly used; this is known as Chomsky Normal Form.