Imagine a world where anyone can take anything from anyone else, anytime. You plant a garden, and a stranger harvests it. You build a house, and a passer‑by moves in. In such a world, why would anyone bother to plant or build? That thought experiment reveals why property rights are the invisible foundation of economic life. This chapter explains where those rights come from, what they really are, and how their design can help people cooperate or lead to big trouble.