International investment law seeks to promote predictability and stability in host state regimes by protecting investors and, as a result, encouraging them to invest. State initiatives to address climate change necessarily involve changes to those regimes. This chapter explores how climate change initiatives can conflict with basic investor protection guarantees found in virtually every investment treaty. It then describes how some recent treaties give host states more flexibility to adopt climate change measures. Finally, this chapter examines recent investor-state arbitration cases in which investors are seeking compensation for losses they have suffered when states renege on commitments intended to encourage investment in climate change mitigation, such as feed-in-tariff (FIT) rate guarantees. These cases illustrate how the stability in host state regimes resulting from investment treaties might support rather than undermine climate change initiatives, although at the cost of host state flexibility to respond to changes in energy demand, fuel prices, and budgetary and other pressures. Overall, much work is needed to adapt investment treaties to the distinctive features of the relationship between climate change and investor protection if they are to support climate change mitigation.