This chapter considers the idea of constitutional identity as it pertains to the UK, viewed from the perspective of EU-UK relations. The analysis begins by consideration of the conceptual frame within which the relationship between UK and EU law evolved, and more especially the way in which supremacy was conceived in EU law and UK law, respectively. The discussion thereafter shifts to a more general consideration of the idea of constitutional identity in the UK. While the language of constitutional identity is not commonly used in judicial discourse, there are nonetheless a number of precepts that are central to the identity of the UK constitutional order. These include parliamentary sovereignty, constitutional statutes and the principle of legality, the rule of law, and devolution. The analysis then shifts to the consequences of a clash between EU law and UK law that impacts on one of the preceding UK constitutional precepts. These consequences may be interpretive or substantive in nature, and they are examined in turn. Brexit, however, means that it is unlikely that the issues raised in the last section of the chapter will be tested.