Most investment protection treaties includes a provision on fair and equitable treatment. The provision is included to ensure an investor from one of the contracting states a minimum level of treatment in the territory of the other, unrelated to the treatment of national investors. The fair and equitable treatment standard is intrinsically connected to the minimum standard in customary international law. The provision has proven difficult to interpret, and case law on the matter has been substantial during the last five years. In this thesis three interconnected themes are discussed; what level of treatment is guaranteed by the fair and equitable treatment standard? What is its relationship to the minimum standard of treatment in customary international law? And what impact does the development regarding the fair and equitable treatment standard have on customary international law?