To establish defensible, legitimate expectations, investors in the energy sector must undertake extensive assessments of the political, economic and social landscape. A key feature of this landscape will be the host state’s commitment to mitigating the effects of climate change. This is of course relevant in relation to claims by traditional energy investors (in the coal, oil and gas industry) where states have implemented measures designed to reduce carbon emissions or promote renewable energy production. However, investors in green energy production must also have regard to the possibility of regulatory and legislative change, and – absent a clear commitment by the host state – cannot expect stability by virtue of global trends alone. This paper will examine the interpretation of ‘legitimate expectations’ in recent claims under the Energy Charter Treaty, and consider how tribunals are likely to balance the state’s sovereign right to regulate against the investor’s need for stability in the future.