The plenary courts of Alfonso VIII of Castile (1158–1214) have not been studied in depth by his biographers, nor by those interested in the early history of parliamentary assemblies, yet their function, composition and frequency reveal interesting aspects in the dynamics of institutional change and the relationship between the monarchy and the aristocracy. These courts became an important instrument for the centralisation of governance; their political relevance is clearly recognised in the commemorative clauses of some royal diplomas, but has been generally overlooked by scholars more concerned with constitutional landmarks and parliamentary developments. The present study will address the institutional nature and political importance of the great courts summoned by Alfonso VIII, from the great court of Burgos in 1169 to that of Carrión de los Condes in 1188, gatherings that served to publicise two crucial moments in his long reign: the coming of the king’s majority, and his consolidation as an Iberian leader.