In recent decades an infusion of economics has lent the study of strategy much needed theory and empirical evidence. Strategy consultants, armed with frameworks and techniques, have stepped forward to help managers analyze their industries and position their companies for strategic advantage. Strategy has come to be seen as an analytical problem to be solved. But, says Montgomery, the Timken Professor of Business Administration at Harvard Business School, the benefits of this rigorous approach have attendant costs: Strategy has become a competitive game plan, separate from the company's larger sense of purpose. The CEO's unique role as arbiter and steward of strategy has been eclipsed. And an overemphasis on sustainable competitive advantage has obscured the importance of making strategy a dynamic tool for guiding the company's development over time. For any company, intelligent guidance requires a clear sense of purpose, of what makes the organization truly distinctive. Purpose, Montgomery says, serves as both a constraint on activity and a guide to behavior. Creativity and insight are key to forging a compelling organizational purpose; analysis alone will never suffice. As the CEO--properly a company's chief strategist--translates purpose into practice, he or she must remain open to the possibility that the purpose itself may need to change. Lou Gerstner did this in the 1990s, when he decided that IBM would evolve to focus on applying technology rather than on inventing it. So did Steve Jobs, when he rescued Apple from a poorly performing strategy and expanded the company into attractive new businesses. Watching over strategy day in and day out is the CEO's greatest opportunity to shape the firm as well as outwit the competition.