The theory of formal languages is widely accepted as the backbone of t- oretical computer science. It mainly originated from mathematics (com- natorics, algebra, mathematical logic) and generative linguistics. Later, new specializations emerged from areas ofeither computer science(concurrent and distributed systems, computer graphics, arti?cial life), biology (plant devel- ment, molecular genetics), linguistics (parsing, text searching), or mathem- ics (cryptography). 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 – in its two basic forms, natural and arti?cial – is a particular case of a symbol system. This wide range of motivations and inspirations explains the diverse - plicability of formal language theory ? and all these together explain the very large number of monographs and collective volumes dealing with formal language theory. In 2004 Springer-Verlag published the volume Formal Languages and - plications, edited by C. Martín-Vide, V. Mitrana and G. P?un in the series Studies in Fuzziness and Soft Computing 148, which was aimed at serving as an overall course-aid and self-study material especially for PhD students in formal language theory and applications. Actually, the volume emerged in such a context: it contains the core information from many of the lectures - livered to the students of the International PhD School in Formal Languages and Applications organized since 2002 by the Research Group on Mathem- ical Linguistics from Rovira i Virgili University, Tarragona, Spain.