One of the main catalysts for the shift towards renewable energies has been the practice of support schemes in a key number of EU member states. Some of these states have since withdrawn or revoked much of their original support, which has resulted in investment treaty arbitrations being filed against them under the Energy Charter Treaty. Arguably, a balance should be found between investors’ legitimate expectations concerning the stability of the legal framework and the host states’ right to adapt regulations to new needs. This can be achieved by clarifying and delimiting the principle of fair and equitable treatment, and by encapsulating it in a more precise set of rules. Due to its open character, this principle could otherwise become too intrusive a standard of judicial review for the exercise of sovereign power by host states. It could be diluted into a rhetorical framework inviting uncertainty and subjective judgment. While the focus of this article is on energy, the concern for legal stability equally applies to all those sectors where large upfront investments are required, which can only be recouped in the long run.