This chapter describes the conceptual and theoretical background on which the directors of the IBE based their action. Rosselló, deputy director, was a pioneer in comparative education that, for him, was a way of relating the particular with the universal, to draw up international and even universal prospects by taking into account local and regional data. The IBE was a worldwide centre for comparative education, removing any spirit of caste or class. As for Piaget, he transposed his theoretical model of development from egocentrism to reciprocity taking into account the point of view of others. This reciprocity allows “the ascent from the individual to the universal”, to build unity in diversity, universality without uniformity. The insert on the documentation frenzy of the IBE shows another lesser known aspect of IBE activities.