The Transition is one of the fundamental events of the Spanish 20th Century. We have the stage that will host the decline and fall of the Franco dictatorship, the regime that had reigned in Spain for the last 40 years, and the advent and consolidation of the parliamentary monarchy of Juan Carlos I. It is a really intense period in which a wide variety of economic, social, cultural and political factors would result in a strong State crisis. After the succession that followed Franco's death the King was in a very adverse situation, striving to implement a reformist constituent process that managed to overcome the dangers that threatened his position as King and head of State. Eventually Adolfo Suárez would end up standing out in history as the man who would lead the constitutional process successfully, neutralizing on one hand the disruptive strategy of the anti-Francoist opposition and on the other the continuity strategy championed by the more orthodox Francoist. His main achievement was to get a pact between the francoist forces and the antifrancoists, the new consensus allowed to articulate the drafting of a new Constitution with the main political parties that emerged during the transition. The transition had as a result the legitimacy of the monarchy and the new regime. The democratic legitimacy provided by the anti-Franco opposition was key primarily thanks to the PCE and PSOE, because without their participation the reform had not been able to succeed because of the serious State crisis that the Franco regime was going through. The popular consultations of the law for political reform, elections in June 1977, the referendum on the Constitution and elections in 1979 were also essential to the legitimacy of the process. In regards of the Pact the main result is the adoption of the State parties model predominant in Western and continental Europe. In this sense Spain gets matched with the political situation in Europe, also inherited from the context of the Cold War that still lived during those years that decisively influencedw the Spanish Transition too. ; Grado en Historia