The environments of space are lethal, mandating a variety of control and safety structures, some of which will be much more pervasive, and potentially intrusive, than on the Earth. Protecting, and even defining freedom , in these environments constitutes an important development in political philosophy. In this volume of essays, we discuss a set of ideas that range from the philosophical foundations to the policy implications of extraterrestrial liberty . The breadth of discussion is by no means exhaustive, but it does reveal the potential for a long and controversial discussion on freedom that is likely to follow humans into space and remain with them for as long as they attempt to settle the space frontier.