Formal language theory is widely accepted as the backbone of theoretical computer science. All human problem solving capabilities can be considered in some sense as the manipulation of symbols and structures prepared by the symbol, which is actually the stem of formal language theory. Contributors presents the main results and technical fields of specialization in a way that is easily accessible along with many references have a dual role: history, instructions to complete evidence or solutions to exercises, guidance for further research in which readers can identify the problem interesting. We believe that the volume represents "the gateway to the formal language theory and its applications", will also be useful as a general source of information in the theory of computing, both at the undergraduate level and research.