Rare indeed are chief executives who don't launch at least one major organizational transformation during their tenure—to catch up with other companies, to recover from a crisis, to get the best from an acquisition or a merger, or just to stay on top. In today's business environment, incremental improvement is seldom enough.

But for all that has been written about change, no one formula can make it successful. The most important factor is often a CEO's ability to create, sustain, and channel the organization's energy. Releasing it requires broad-based action: creating the right architecture for the change program, emphasizing both near-term performance and longer-term health, setting the right aspirations and creating a time line to meet them, embedding change in processes and systems, transforming the behavior of employees, and renewing the senior-management team. This is indeed no small challenge—no other kind of effort requires such strong leadership from the top to make the right impact.

As part of The McKinsey Quarterly's efforts to understand the process of corporate transformation, we have talked with a number of successful executives in the past year or so about their experiences and insights. A complete listing of these interviews are available on our Web site. This edition of the Quarterly features another installment in the ongoing series: Giancarlo Ghislanzoni's conversation with Paolo Scaroni, the CEO of Eni.

Scaroni is remarkable for having overseen three separate performance transformations: a largely operational turnaround at the UK glassmaker Pilkington from 1997 to 2003; a portfolio restructuring of the leading Italian electricity utility, Enel; and an as-yet-unfinished reorganization of the high-flying Italian energy group Eni. His reflections on the differences between these transformations make for instructive reading. As Scaroni says, "I normally try to find three or four strategic concepts that sum up the direction in which the company should be moving, build up an organization that believes in these concepts, and then repeat, repeat, and repeat them throughout the organization. Successful things are simple; I have never seen successful things that are very complicated."

During Scaroni's time at Enel, he simplified its business portfolio by closing or reincorporating a series of embedded service businesses that his predecessor had launched. Shaping the business mix to align it with favorable macroeconomic trends is also the theme of this edition's cover story: "Going from global trends to corporate strategy," by Wendy M. Becker and Vanessa M. Freeman. As this article makes clear, it's seldom enough merely to follow the trends of the day. To discover the right mix of businesses for the corporate portfolio, companies must closely study the interactions of subtrends and the competitive forces they generate.

Performance transformations are among a chief executive's most challenging and potentially rewarding moves. We hope that our interviews with business leaders on this topic will provide a valuable resource for CEOs contemplating their own corporate transformations.