Chapter 8 analyses perhaps the most sensitive and controversial part of the Trade and Cooperation Agreement, the Protocol on Northern Ireland. Graham Butler examines the tensions created by the Protocol, in particular, the question of cross-border trade between Northern Ireland and Ireland. He examines what this arrangement means for Northern Ireland's relationship with both the UK and EU by focusing on the continued relevance of the EU customs union, the free movement of goods, and the enforcement mechanisms. In doing so, he analyses the intricate position of the Protocol as regards the trade in goods in the form of how the EU customs area is extended to Northern Ireland, and the implications this has on different types of trade in goods with Northern Ireland, as well as the type of regulatory alignment envisaged by the Protocol.