Many IIAs contain obligations that prohibit host state discrimination against foreign investors. These may be framed as obligations not to favour any country’s investors over the investors of the parties to the IIA (most-favoured nation [MFN] treatment), or as obligations to treat foreign investors no less favourably than domestic investors (national treatment). This section considers how these obligations might be framed in a way that gives host states certainty about the nature of their MFN and national treatment obligations, and that allows them to pursue legitimate environmental objectives.