For centuries, scholars have wrestled with seemingly intractable problems about the nature of property. This Article offers a different approach. Instead of asking what property is, it asks what property does. And it argues that property protects people’s reliance on resources by moderating the pace of change. Modern scholarly accounts emphasize voluntary transactions as the source and purpose of reliance in property. Such “transactional reliance” implies strong, stable, and enduring rights. This Article argues that property law also reflects a very different source of reliance on resources, one that rises and falls simply with the passage of time. This new category of “evolutionary reliance” is at the heart of core property doctrines like adverse possession, waste, and the rule against perpetuities. Focusing on evolutionary reliance reveals a new vision of property, not as a bundle of sticks or a bare right to exclude, but instead as a nexus of competing and dynamic reliance interests that can change over time. This new vision has important conceptual and doctrinal consequences for common law doctrines and the Takings Clause, and it highlights the surprising dynamism and change in property.