The communitarian theory of WTO law outlined in previous chapters works reasonably well as a description of key features of WTO law. Its “fit” with the existing law raises the possibility of the theory serving wider applications. That possibility is likely to be canvassed most insistently in relation to international investment law, the body of law pertaining to the protection and treatment of foreign investment by host states. A communitarian theory would forecast international investment law to be preoccupied with corrective justice and to be heavily contractual, retrospective and inductive. The chapter demonstrates how all of these features are confirmed in the shape of contemporary international investment law, and how in light of considerable dissatisfaction with the current investment regime, an impulse is detected toward something more egalitarian, and therefore more obligatory, constitutive, prospective and presumptive.