I Logical and Algebraic Preliminaries.- I Words - Monoids - Languages.- II. General Definition of Formal Systems.- III. Combinatorial Systems.- IV. Algorithms - Turing Machines.- V. Computability - Decidability.- VI. Combinatorial Systems and Turing Machines; Undecidable Problems.- II Some Important Classes of Languages.- VII. Context-Free Languages.- VIII. Undecidable Properties of CF-Grammars.- IX. Push-Down Automata.- X. Kleene Languages and Finite Automata.- XI. Languages Defined by Systems of Equations.- XII. Context-Sensitive Grammars. Linear Bounded Automata.- III The Algebraic Point of View.- XIII. Homomorphisms of Monoids.- XIV. More about Kleene Languages.- XV. More about Context-Free Languages.- XVI. Algebraic Languages.- Transformational Grammars.- Bibliography of Transformational Grammars.- Annotated Bibliography.