||This book defends political obligation, stating that people are morally obligated to obey the law of their state, if the law is at least reasonably just. The defense is based on the tradition of the Kantian political philosophy and legal philosophy, and it is a defense mainly against political anarchists. They believe that the only possible justification for political obligation should be voluntarist, proving people’s deliberate undertakings to incur the obligation. Since no attempt in the voluntarist approach is justifiable, political obligation does not exist from the a posterior point of view. As a consequence, political legitimacy, which is claimed to be the other side of the same concept of political obligation, fails to obtain its justification, and no state is legitimate. The exploration in this book contends that a voluntarist basis is neither necessary nor sufficient for people to be obligated to obey the law. And this contention earns the space for justifying political obligation on an involuntarist ground, meaning that people can be imposed on a moral obligation to obey the law without any voluntary actions incurring this obligation. This involuntarist ground is what I name the “moral necessity thesis”.