The Intergovernmental Panel on Climate Change has suggested that annual greenhouse gas (GHG) emissions must be cut 50 to 80 percent worldwide by 2050 in order to stabilize the climate and avoid the most destructive impacts of climate change. California governor Arnold Schwarzenegger and U.S. president Obama lined up behind this goal. Yet the strategies for meeting these ambitious economy-wide targets have not been clearly defined, and the technology and policy options are not well understood. This chapter explores how such deep reduction targets (50 to 80 percent) could be met in the transportation sector by 2050, with a focus on California and the United States as a whole. It presents a framework for understanding emission reductions in the transportation sector, lays out the major mitigation options for reducing emissions, and presents scenarios to explore how deep reductions could be achieved. Additionally, this chapter also presents an analysis that looks at the transition scenarios for vehicles in the light-duty sector to investigate how they may evolve from the present fleet to achieve the deep-reduction scenarios by 2050.