If you leave your bike unlocked outside a busy café, you might have a pretty good guess about whether it will still be there when you come back. You weigh the chance of theft against the inconvenience of locking it. This chapter turns that same cold-eyed calculation around and asks: what does the would-be thief think about? By modeling crime as a choice—not a sickness or a moral failing—we can start to see how law shapes behaviour, and how much punishment is enough, but not too much.