In this introductory chapter to Part II, we will examine the key specifics of the EU legal order and investment protection mechanisms under EU law, with a view to expose systemic similarities and differences between the EU legal order and international investment law (IIL). First, we will explain the basic features of the EU legal order. Second, we will expose the modus operandi of the EU judicial system and the Court of Justice of the European Union (CJEU) as its integral part. Finally, we will explain the scope of investment issues in the EU legal order to understand the reasons which render IIL more attractive to intra-EU investors than EU law. This chapter thus provides the context to the discussion on intra-EU dispute settlement in the next chapter. The divergent approaches to intra-EU ISDS between investment tribunals and the CJEU epitomise the fundamental differences of the two legal orders discussed in this chapter. The tensions between these two legal orders can only be understood in light of the constitutionalisation of the EU legal order, the process in which the CJEU plays the key role.