This specialized book examines the impact of Bilateral Investment Treaties (BITs) as instruments for regulating the treatment of foreign investments. It highlights the historical doctrinal divide between capital-exporting and capital-importing states, particularly in the context of multilateral failures and bilateral successes that led to the proliferation of BITs as part of customary international investment law. The work addresses the paradox of consensus on BITs and analyzes the significant role of arbitration, which is viewed as a privatization of international law. It also focuses on the increasing dilemmas faced by host states, especially regarding the need to take measures to protect essential security interests, even if this may conflict with the provisions of the treaty.