This text book is designed for the first course in Theory of Computation & Application (Automata Theory and Formal Languages) for the students of B.Tech. (CS/IT) and Master of Computer Applications (MCA) programs of Uttar Pradesh Technical University (UPTU), Lucknow, as well as other Indian Universities. At the end of each chapter a summary for quick revision of concepts and an exercise consisting of objective questions, review questions and programming problems have been given.