Since 1980, Michael Porter's classic Competitive Strategy has provided the methodology that most big companies use for strategic analysis. But now, distinguished Columbia Business School professor Bruce Greenwald offers a bold new theory of competition - a theory that is far simpler than Porter's and much easier for strategic planners to apply in the real world. Porter identified a complex five-force model for studying competition in any market. But Greenwald argues that there is only one essential factor in determining competitive advantages: how easy it is for competitors to enter or expand in a given market. If a company can erect strong barriers to entry - through customer captivity, lower production costs, or economies of scale - it can manage these advantages, anticipate competitors' moves, or achieve stability through bargaining and cooperation. Greenwald draws on game theory to explain what you should do if barriers to entry are strong, weak, or nonexistent. He covers a wide range of examples, from retail to telecommunications to auction houses. And his lessons can be applied whether your business is dominated by a single huge player, a handful of roughly equal players, or no one at all.