For a long time, international investment law was solely a law for the promotion and protection of foreign private investment. National laws as well as the first international investment agreements had established a legal regime that was extremely favorable to foreign private investors. Today, the evolution of international investment law no longer justifies this overprotective regime for foreigners and their investments. In fact, host states have become aware of the increasing erosion of their economic sovereignty resulting from their contractual and treaty commitments relating to the protection of foreign assets. This is why they are increasingly interested in safeguarding their normative freedom. On the basis of this observation and in the light of the study of the substantive rules of international investment agreements, this textbook course aims not only to give an account of the threat to the normative power of States hosting international investments, but also to propose the modalities of a necessary preservation of this normative power.