Only humans learn concepts like atom, integer, and democracy. But by all appearances, these abstract ideas are not present in the initial human state when babies are born. Other concepts like object, cause, or agent may be present early in infancy, if not innately. This volume explores the controversial science of human conceptual development, a traditional battleground for debates surrounding human nature. Are humans born good and tainted by an imperfect world? Or do we need to teach children to be moral? Could a concept like freedom be woven into the human soul, or is it a historical invention, constructed over generations of humans? What does it mean for a concept to be innate? Or for a concept to change? Are humans fundamentally different from other animals in how we think and reason about the world? The growing science of conceptual development seeks to explore these issues by targeting two specific questions: (1) Which human concepts constitute innate, core, knowledge? and (2) How do humans acquire new concepts, and how do these concepts change in development? This volume, written almost exclusively by developmental psychologists, documents key advances in case studies that address these questions, including ground-breaking science on language, moral reasoning, causal explanation, and human representations of objects, number, events, color, space, time, and other minds.