Deontic logic deals with obligation, permission and related normative concepts. This textbook introduces three frameworks that have dominated the landscape of deontic logic: monadic deontic logic, dyadic deontic logic, and input/output logic. It describes their language, semantics, proof theory, and gives soundness and completeness theorems. The addition of exercises makes the book ideal for self-study or as a textbook in class. Deontic logic remains neutral on application issues. Over the years, it has been applied in a variety of fields, including philosophy, ethics, linguistics, computer science, and the law. This textbook will serve as a valuable resource for students and researchers wishing to gain a practical understanding of deontic logic for use in their work.