Deontic logic is the logic of obligations, prohibitions and permissions. More conceptually, it is the logic of ideal states of affair versus actual states of affair. As such it is a foundation of law, but also of normative systems and normative multi-agent systems, where agents are susceptible to norms while acting. In this course we will see how deontic logic can be viewed as a branch of modal logic. In order to deal with problems of proper representation, such as the infamous paradoxes of deontic logic, researchers have looked for alternative formalisations such as dyadic deontic logic and non-normal modal logic. In this course based on the book mentioned below, we will also look at a very abstract and general way of treating deontic logic, viz. input-output logic as proposed by Makinson and Van der Torre.