This is an essay of intellectual and conceptual history. It’s constructed in reverse: from the present to the past. The objective is to demonstrate the socio-political origin of some analytic categories employed by the Social Sciences and Humanities. In the evolution and transformation of the term mestizo to more generic use of the term mestizaje, five overlapping semantic layers can be observed. The article shows the places in which the term mestizaje, a modern concept, progressively changed beginning at the end of the 19th century to a key referential term of national identity in Mexico. The diffusion and consolidation of the notion mestizaje occurs paradoxically in a moment (during the first half of the 20th century) when humanity began to be thought of in global or post-national terms. From then on the use of the term pretends to designate not only exclusively the essence of the “Mexicanidad” but also represents Latin American identity.