Imagine a group of competing firms deciding that life would be much easier if they stopped fighting for market share and simply agreed to raise prices together. That secret handshake sounds tempting — until one of them is tempted to break the promise, grab a bigger piece of the pie, and trigger a price war. This chapter is about why firms sometimes succeed in cooperating against their customers, why such agreements so often fall apart, and how smart policy can make cheating the better option.