The General Estoria, written in the thirteenth century on the initiative of Alfonso X of Castile, is the most ambitious world history of the European Middle Ages. It took more than two decades to translate and combine the more than one hundred Latin, French and Arabic sources into a complex work. After the king’s death, and with the work still unfinished, the original redactional team scattered; the Estoria was not copied or read as a whole for the following few centuries, although various sections knew a limited success in the period up the sixteenth century. Until 2009, no complete scholarly edition of the work was available; only the First, Second and sections of the Third had been edited. 2009, a team of philologists (including the authors of this article) published a critical edition of the entire work. The theoretical basis for this edition is presented in this article.