This book provides a critical introduction to the principles and institutions that make up the Spanish Constitution, which was enacted in 1978. It first explains the process of transition from Franco's dictatorship to democracy, in order to understand the historical circumstances under which the Constitution was framed. After offering a theory to justify the authority of the Constitution over ordinary laws, the book proceeds to explain the basic principles of the Spanish political regime, as well as the structure of its complex legal system. Later chapters focus on various institutions, such as the Crown, Parliament and the Government. A specific chapter is devoted to the territorial distribution of power between the State, the regions and local government. The last two chapters deal with the constitutional role of courts, and the protection of fundamental rights. The book includes some reflections on the challenges that lie ahead and the constitutional reforms that may need to be considered in the future.