This chapter discusses the disappearance of the Union del Centro Democratico (UCD) and the accession to power and opposition of the Platform of Democratic Convergence linked in common cause the Socialist party (PSOE) and the Alianza Popular, respectively. The PSOE began its move toward the center in 1979. By the general elections of 1982, the PSOE had drawn sufficiently close to the center to pull former UCD voters into its ranks and thus assure a Socialist victory. The centripetal process of moderation in the some major national parties is the key element to understanding Spanish political parties since 1979. The chapter describes the proliferation of parties in the Spanish multiparty system, at both at the national and the regional levels. The major characteristic of the system is its youth; for all practical purposes, Spanish political parties came into being after January 1977.