Some understandings of European Union health law are based on a presumption of law as a static and closed system. This approach to the Union as a legal entity has important ramifications. The Union is a political system created by and subject to the rule of law. Its successes (and failures) are attributable to the legalisation of solving externalities and ensuring Member State solidarity to gain benefits from integration. Member States, which create and sustain the Union by repeated acts of sovereign choice, choose to subject themselves to the rule of (Union) law. This protects both the Member States and the Union institutions (imperfectly, but nonetheless) from charges of illegitimacy. While recognising the benefits of such an approach to European Union integration and law-making, we take the view that law also has an important dynamic potential. That dynamic potential is inherent in all law, for law is embodied in text, and always open to interpretation, as the external contexts that give legal text meaning in the real-world change through time. We trace the dynamic potential of Union health law by looking at its legal basis to its foundational Treaties, and we plot its trajectory going forward.