The relation between administrative law and the Constitution is a traditional topic in Spanish public law. The paper explores three perspectives. First, the interaction among administrative law and the Constitution shall be studied. The latter has many effects on the former, but the process also operates the other way around. This is partially fostered by the long-standing tradition of codification of administrative law, which strengthens the autonomy of the latter vis-à-vis the Constitution. Secondly, the latter shapes the basic structures of administrative law. But, from a comparative standpoint, a peculiar feature lies in the fact that it also governs the substance of many administrative policies. Finally, the constitutional function of EU law shall be touched upon. EU primary law and national Constitutions reciprocally influence the manner in which they steer the development and implementation of national administrative law. This paper will focus on the top-down interaction.