When an owner of capital invests in their ‘home’ state, this investment is governed by national law. But when an investor exports their capital, a whole extra body of law supplements, and sometimes supplants, these domestic arrangements. This is international investment law (IIL): the vast body of investment agreements; arbitral decisions; and other forms of hard and soft law that protect the rights of foreign investors in ‘host’ states. Flynn and Lawrence critique IIL from a material constitutionalist perspective, revealing an order bound up with the history of imperialist expansion; the inscription of the rights of the investor class as general and international; and a desire to protect capital and markets from state interference. IIL is currently undergoing a ‘constitutional crisis’, but though reforms may improve certain serious flaws, material constitutionalist analysis reveals inherent features that cannot be reformed without fundamental reconfiguration of the material relations between international capital and state constitutional orders.