Both the foreign investor and the host state government are concerned with certainty and predictability of their relationships. They need to be sure that the other party complies with its promises. They usually try to attain this by entering into concession agreements. In fact, signing an agreement by itself cannot be a guarantee for a party as to performance of obligations undertaken by another. In practice, host states, through exercise of their sovereign powers, have frequently breached concession agreements. This practice is largely reinforced by the view that concession agreements are subject to national laws of host states. The purpose for which concessions are entered, many argue, requires that such agreements be subject to a legal regime external to both parties, i.e., international law. Thus, whether national law or international law applies to concession agreements has remained unresolved issue. This work examines in detail views and facts on both sides of the issue, and makes suggestions as to how the issue should be resolved. As such, the importance of the book for governments, academia and business community is high.