Abstract

International investment law faces five core legitimacy challenges: the state-dependency challenge, the human and constitutional rights challenge, the equality challenge, the standard of protection challenge, and the investor state dispute settlement system challenge. This article endorses the claim that constitutional courts can contribute to the solution of those legitimacy challenges when they exercise the power to review the constitutionality of international investment treaties. From a transformative perspective, constitutional courts of host states can: (i) create public deliberation and raise awareness concerning the legitimacy challenges of international investment law; (ii) grant equal treatment to national and foreign investors; (iii) require governments to negotiate balanced and less open-textured provisions in international investment treaties; (iv) safeguard the protection of human and constitutional rights, and other common goods; and (v) raise due process, predictability, transparency, and proportionality standards concerning the investor state dispute settlement system. These judicial undertakings can strengthen the bargaining power of host executive branch authorities in the negotiation of international investment treaties and can narrow down the space of discretion of international investment arbitral tribunals. Both outcomes could render international investment treatises’ creation and enforcement more legitimate.