Good sex might be priceless, but there’s still a market for it. Ideally, such a market doesn’t involve money—but demand is rampant, supply plentiful, and the exchange goes on every day in every way.

Noah Smith is a former Bloomberg Opinion columnist. He was an assistant professor of finance at Stony Brook University, and he blogs at Noahpinion.

I would like to thank V. Jog, J. Mintz, J. Poterba, and especially an anonymous referee, as well as seminar participants at the Bank of Canada and the Federal Reserve Bank of Cleveland for helpful ...