This dissertation analyzes the emergence of race in the early modern Spanish Empire, from 15th-century Iberia to 16th-century Mexico. In it, I show how race grew out of prior notions of religious difference and argue that this new, racial mode of difference prompted a transformation in European understandings of time and history. I highlight how the racialization of Indigenous peoples was connected to that of Jews, Moors, and Africans, tracing how the early development of racial ideologies worked in and through time. I begin by analyzing the events and controversies surrounding the enactment of the first blood purity statute, the Sentencia-Estatuto of 1449, which targeted Jewish converts to Christianity. I argue that it posed a fundamental challenge to the belief in the effectiveness of conversion and upended medieval understandings of Christian subjecthood. Blood purity policies subsequently informed debates regarding the nature (and thus the rights) of Indigenous peoples. The second chapter focuses on the entrenchment of those distinctions, analyzing how thinkers like Bartolomé de las Casas and Francisco de Vitoria attempted to justify the enslavement of Africans while condemning that of Indigenous peoples in the Americas. The third chapter turns to how Martín de Azpilcueta, one of their contemporaries, theorized the relationship between trade and sovereignty and argues that novel theories of just war and just prices were central to the racialization of slavery and colonization. Chapter four further explores how missionaries like Gerónimo de Mendieta, José de Acosta, and Gregorio García legitimated racial hierarchies. I look to their humoral and climatological theories of difference and argue that notions of blood purity and Iberian figures of otherness—such as Jews and Moors—were fundamental to shaping racial categories in the Americas. The final chapter details the role of race in reshaping European conceptions of time and history. Emergent notions of civilizational development took racial difference to correspond to temporal distance, with races situated as relatively more or less advanced than others. Through this, I track the ways in which time has become a significant site of political struggle.