A question that has arisen in the cases concerning tax rulings that have been brought by the European Commission is whether or not the arm’s length principle is an autonomous standard under EU law. This article seeks to explain why there is no autonomous EU arm’s length principle, or, if there were one, that this would have profound constitutional implications. In short, an EU arm’s length principle would drastically undermine the fundamental constitutional principle that taxes must be levied with the consent of the national legislature.