Charles S. Cockell argues that beyond Earth, space is especially tyranny-prone. Yet rather than consign humanity to a dim future of extraterrestrial despotisms, he suggests that the construction of free societies is possible using uniquely blended and reformulated classical liberal ideas for the space frontier. Interplanetary Liberty offers an engaging exploration of liberal political thought applied to human space expansion, and in so doing provides a much-needed examination of the scope and fitness of democratic principles of governance for prospective space societies.