Formal language theory is a theoretical discipline in computer science that plays a foundational role in areas such as compilers design, programming language theory, information transmission, computational biology, etc.This unique volume is a succinct introduction to formal language theory suitable for an one-semester course. The main focus is on Chomsky's hierarchy of classes of languages ranging from regular languages to context-free, context-sensitive, and recursively enumerable languages. These classes are presented using both generative methods (grammars) as well as various analytical methods including finite automata, pushdown and linearly bounded automata, and Turing machine.The useful reference text contains a large number of exercises of various degree of difficulties and is intended as a textbook for an upper-level undergraduate or a graduate course in formal languages.