In international investment law, the prism of indirect expropriation includes a broad range of measures - such as regulatory measures - which do not involve a transfer of property but result in a serious interference with an investment. the definition of compensable taking is a very sensitive issue situated at the crossroads between the protection of investor's private rights and the safeguarding of the state's sovereign prerogatives. this book explores, through the example of environmental regulation, the law applicable to this controversial topic. It suggests that the traditional approach - based on an extension of the concept of expropriation - is inappropriate and it contributes to clarifying the scope of the international protection of the investor on the ground of the law of state responsibility.