The first time I bought virtual money, in October 2017, bitcoins, the cryptocurrency everyone by now has heard of, were trading at $5,919.20. A month later, as I started writing this, a single coin sold for $2,000 more. “Coin” is a metaphor. A cryptocurrency such as bitcoin is purely digital: it is a piece of code—a string of numbers and letters—that uses encryption techniques and a decentralized computer network to process transactions and generate new units. Its value derives entirely from people’s perception of what it is worth. The same might be said of paper money, now divorced from gold and silver, or of gold and silver for that matter. Money is a human invention. It has value because we say it does.