Investment activity and the economic policies of host States are directly related. This relationship has an impact not only on the attraction of foreign direct investment, but also on the negotiation and conclusion of international treaty law on investment, taxation and trade. The result of the interaction between these different fields of economic law is that tax disputes can be shifted to investor-State arbitration in claims of expropriation. Thus, a fiscal measure can be tantamount to expropriation under international investment law. However, arbitral case law treats taxation as a special category. The general standard of indirect expropriation is then applicable with a higher threshold. This development of the theory of indirect expropriation in fiscalibus is understood from the sovereignty paradigm. When not excluded, the host State's policy space for addressing fiscal issues is restricted by the substantive protection of the investment as covered by the applicable law.