This chapter examines the concept of constitutional identity of the EU from the perspective of public law. As the term appears in the TEU and, in the last 15 years, has been used by different apex courts, it draws on the trend of using constitutional identity as a legal argument against EU obligations or creating constitutional law arguments for this purpose. Thus, the chapter claims that the mandate to respect constitutional identities, as stated in Article 4(2) TEU, finds a limit in the respect for EU constitutional identity. The chapter argues that the EU constitutional identity could be identified in the same manner most Member States identify constitutional identity. Therefore, it argues that constitutional identity is a concept both applicable to the EU and the EU Member States, and to make these concepts compatible, Member States’ constitutional identities are to be respected as long as they are not incompatible with EU constitutional identity, consisting of fundamental principles of constitutionalism.