The first shot in what historians may someday commemorate as the Great Pizza War was fired by Domino’s in late 2009. The chain had been charging about $9 for a medium two-topping pizza, but to boost sales it began offering recession-weary consumers two of its two-topping pies for $5.99 each. Several weeks later Papa John’s and Pizza Hut fired back, offering large three-topping pizzas for just $10—at least a third less than the usual price. Soon they improved the deal, so that customers could buy a large pizza with unlimited toppings for $10. Sure enough, sales at all three chains rose—and even now many chains are offering discounted pizzas.

A version of this article appeared in the January–February 2011 issue of Harvard Business Review.