The document summarizes some key constitutional peculiarities and political parties in Spain. It notes that Spain's constitution pushes for social and economic rights and defines the country as a social market economy. It also discusses Spain's territorial organization as autonomous communities and the shifting dominance of centrist, leftist, and right-wing parties over time. It then provides more detail on the three main national parties - the center-left PSOE, the conservative PP, and the left coalition IU. It concludes by outlining some important regionalist parties like the PNV in the Basque country and CIU in Catalonia.