There is growing academic attention being directed towards the technical and engineering issues that face human spaceflight in respect of a journey to Mars. Often overlooked in such discussions, however, are the legal and ethical underpinnings that are needed to regulate human behaviour on such an extraordinary mission. This chapter will examine key issues in respect of law and ethics that will face humans on a long duration spaceflight and any subsequent human habitat or colony. This inquiry will examine the existing framework covering long duration spaceflight aboard the ISS and contrast this with legal issues in respect of the welfare of the crew and potential issues relating to the administration of justice for interplanetary travellers. There will be an analysis of the environmental impact of long duration space activity and the extent to which legal regulation should be used to embed environmentalism as a core mission value. Given that there is an emerging consensus on the damage caused by existing space activities, it is contended that any new regulatory framework should embed a commitment to environmental protection within the fabric of rules governing human behaviour in outer space and should be at the forefront of such policy discussions. It is maintained that such legal and ethical issues are not only vital in respect of any human-crewed mission to Mars, but will become the template for the way in which policy regarding all long duration space flight and constitute the lodestar for normative behaviour in this context.