Mexico of five centuries ago was witness to one of the most momentous encounters between human societies, when a group of Spaniards led by Hernando Cortés joined forces with tens of thousands of Mesoamerican allies to topple the mighty Aztec Empire. It served as a template for the forging of much of Latin America and began the globalized world we inhabit today. This violent encounter and the new colonial order it created, a New Spain, was millennia in the making, with independent cultural developments on both sides of the Atlantic and their fateful entanglement during the pivotal Aztec-Spanish war of 1519–1521. Collision of Worlds examines the deep history of this encounter with an archaeological lens—one that considers depth in the richly layered cultures of Mexico and Spain, like the depths that archaeologists reveal through excavation to chart early layers of human history. It offers a unique perspective on the encounter through its temporal depth and focus on the physical world of places and things, their similarities and differences in trans-Atlantic perspective, and their interweaving in an encounter characterized by conquest and colonialism, but also active agency and resilience on the part of Native peoples.