The Spanish Constitutional Court has been confronted by a secessionist movement posed by Institutions of the Autonomous Region of Catalonia. Through rulings as Decision n. 114/2017, of 17 October [Action of unconstitutionality against the Law of the Catalonian Parliament ‘On Self-determination Referendum‘]; Decision n. 120/2017, of 31 October [Action against the Resolution on nominating members of the ‘Catalonian Electoral Commission‘], and Decision n. 124/2017, of 8 November [Action of unconstitutionality against the Law of the Catalonian Parliament ‘On Legal Transition and Republic‘s Foundation‘], the Spanish Constitutional Court has firmly confirmed the validity of the constitutional principles: national sovereignty belongs the Spanish people (art. 1.2) and unity of the Spanish Nation (art.2) as the basis of the Spanish Constitution of 1978. By requiring the constitutional reform through the procedure set out therein also defended the supremacy of the Spanish Constitution.