The last twenty years have brought forth a body of research known under the names of the theory of automata and the theory of formal languages. Both topics are closely related and form a distinct part of what is rather nebulously described as "computer science." They are made up of a body of mathematical objects, theorems, and methods of proof that are essentially algebraic, bordering on logic. Many of the published results show motivations specific to the interests of their authors and these were frequently very varied—to mention a few: logic, linguistics, theory of communication, programming, electronic circuits, and even models for neurophysiology.