The theory of formal languages is widely accepted as the backbone of theoretical computer science. It mainly originated from mathematics (combinatorics, algebra, mathematical logic) and generative linguistics. All human problem solving capabilities can be considered in a certain sense as a manipulation of symbols and structures composed by symbols, which is actually the stem of formal language theory. Language a" in its two basic forms, natural and artificial a" is a particular case of a symbol system. The contributors present the main results and techniques of their areas of specialization in an easily accessible way accompanied with many references having a multiple role: historical, hints for complete proofs or solutions to exercises, directions for further research where the reader may identify attractive problems. This volume contains areas, mainly applications, which have not appeared in any collection of this type. We believe that the volume representing "a gate to formal language theory and its applications," will be also useful as a general source of information in computation theory, both at the undergraduate and research level.