Imagine a city where rents have doubled in five years. The government steps in and caps rent at $800 a month. That sounds like a win for renters, but soon “apartment wanted” ads pop up and people pay under-the-table fees just to get in the door. Something deeper is going on. In this chapter we see what happens when governments set maximum or minimum prices, and we learn a powerful tool — comparative statics — to figure out where prices and quantities are headed when the world around a market changes.