This chapter examines investment-related aspects of the energy–environment nexus. State actions against fossil fuel investments often have an environmental cause, raising the issue of policy space under the investment regime. The doctrine of ‘police powers’ provides grounds for qualifying some pro-environmental interventions as non-compensable non-expropriatory measures. In addition to seeking policy flexibilities, many States wish energy investors to voluntarily bear social responsibility on the environmental front. As a result, a number of IIAs provide for responsible business conduct, bringing some changes to the ‘investor vs. State’ asymmetry in the investment system. A surge in renewable energy ISDS cases in the last ten years is another noticeable trend. High upfront costs of renewable energy projects recoupable in a long run necessitate FIT or other long-term benefits to investors. But when the government suddenly cancels or cuts promised incentives, this frustrates investors’ legitimate expectations under IIAs but may also be welcomed under trade law as a way of getting rid of distortive subsidies. Thus, some discrepancy or tension between the trade and investment regimes can arise.