Paul Krugman is the winner of the 1991 John Bates Clark Medal, given every two years to "that American economist under forty who is adjudged to have made a significant contribution to economic thought and knowledge." I shall attempt to convey a flavor of Krugman's research contributions, grouped...

It seems that firms behave contrary to the standard economic theory of investment. We observe that firms do not invest as soon a price rises above long-run average cost; instead firms wait until price rises substantially above long-run average cost. On the downside, firms stay in business for...