This chapter analyzes the Jesuit missionary tradition of studying local customs and languages, which is known as “Jesuit anthropology.” By looking into some of the foundational Jesuit texts, the goal is to show how knowledge of non-Christian peoples had been constructed around the metaphor of “living books”: a “stranger” was a book, which the missionaries needed to decipher. From the information, observation, and expertise developed informally in all missionary fields, some Jesuits produced texts—some published but mostly remaining in manuscript—that were and still are considered important pieces in the European library of knowledge. The need and desire to know others was, of course, linked to religious goals: translating Christian message, administering sacraments, fulfilling divine will. From Francis Xavier to Michel de Certeau, the chapter addresses a set of Jesuit perspectives on alterity. They document the richness of interactions between the Jesuits and the local actors, but they always have to be read in light of the Jesuit project of religious conversion.