Investment treaties grant special international protection to foreign investors, and give them a means to enforce those rights against States in which they have invested. This book examines systematically the law of international investment treaties. Although the precise provisions of investment treaties are not uniform, virtually all investment treaties address the same issues. This book examines those issues in detail, including the scope of application, conditions for the entry of foreign investment, and general standards of treatment of foreign investments. The field has seen considerable growth in the number and scope of investment treaties, now estimated at 3300, and investor-state arbitrations cases, which reached over 1000 in 2020. Beyond growth, the field has also experienced significant changes and reforms.