This paper provides an overview of the greenhouse gas emissions from both the marine and aviation transportation sectors, as well as a variety of policies and associated scenarios that could mitigate emissions from these sectors. Though this segment only releases a relatively small proportion of worldwide greenhouse gas emissions, it is projected to grow quickly by 2050 and its emissions are largely unregulated. The paper assesses the relative merits and pitfalls of national legislation such as tradable certificates and international agreements such as the Kyoto Protocol that can be used to reduce emissions from aviation and maritime transportation.