In the compilation of source programs, the second phase of the process is the syntactical analysis. Based on the lexical analysis, the syntactical analysis checks the correctness of the source programs in terms of the grammar of the language used. And it is well-known that most of the properties of the programming languages are context-free. Therefore, naturally if we want to check whether a program is correct or not in terms of syntax, we should check if the syntax of the program is consistent with context-free, at least for most of it. In order to do so, the basis is to know about the context-free grammars. This chapter and Chapter 5 together form the preparation of the syntactical analysis.