Abstract This chapter examines Spain’s successful constitutional transition through the gradual accommodation of territories. It first explains the context that paved the way for Spain’s peaceful transition to democracy during the period 1975–79, from the Civil War of 1936–39 and the dictatorial rule of General Franco to the mobilization of opposition around left-right cleavages and several territorially based nationalist movements, the moment of constitutional transition between 1977 and 1979, and the approval of a democratic Constitution in December 1978. The chapter then describes the period of constitutional engagement from 1978 to 1983 as well as the outcomes of the 1978 Constitution, particularly with regard to its creation and institutional accommodation of seventeen regions and nationalities or “autonomous communities,” elections and decentralization that sought to address regional demands for more autonomy, and devolution. It concludes with an analysis of lessons that can be drawn from Spain’s transition from authoritarianism to democracy.