For a long time, international investment law has emerged as a rather distinct and specific element of international economic law and general international law. The most significant developments in investment law can be considered the negotiations on CETA, TPP, and TTIP, as they imply a ‘generalization’ of international investment law: namely, international investment law is now conceived as providing a legal framework for investments vis-à-vis all States; whereas investment protection sides with trade rules in the common framework of preferential trade agreement. In order to properly address these significant changes, a ‘constitutional’ view is suggested here, which brings into play elements of constitutional thought in order to critically assess both the interfaces between such a ‘generalized’ investment law and the domestic and the EU legal order and its relation to other parts of international law, including human rights and particular questions concerning the context of a right to property.