Margaret Gilbert offers an incisive new approach to a classic problem of political philosophy: When and why should I do what the laws of my country tell me to do? Beginning with carefully argued accounts of social groups in general and political societies in particular, the author argues that in central, standard senses of the relevant terms membership in a political society in and of itself obligates one to support that society's political institutions. The obligations in question are not moral requirements derived from general moral principles, as is often supposed, but a matter of one's participation in a special kind of commitment: joint commitment. An agreement is sufficient but not necessary to generate such a commitment. Gilbert uses the phrase 'plural subject' to refer to all of those who are jointly committed in some way. She therefore labels the theory offered in this book the plural subject theory of political obligation. The author concentrates on the exposition of this theory, carefully explaining how and in what sense joint commitments obligate. She also explores a classic theory