This book investigates the historical development and application of the Spanish concept of 'limpieza de sangre' (purity of blood) and its influence on the colonial Mexican 'sistema de castas'. It explains how this notion, initially used against converts in early modern Spain, was transplanted to the Americas and adapted to create and reproduce identity categories based on descent. The author examines how various institutions in colonial Mexico utilized the concept of purity of blood over time, arguing that its enduring religious, genealogical, and gendered meanings shaped the region's patriotic and racial ideologies.

The book is recognized as the first in-depth study to connect the Spanish concept of 'limpieza de sangre' with colonial Mexico's 'sistema de castas'. It is noted for explaining how this notion was initially used against converts in Spain before being adapted in the Americas to classify individuals based on descent. The work further details how various institutions in colonial Mexico employed this concept, ultimately arguing for its significant role in shaping regional ideologies.