How do you keep the vitality of Day One, even inside a large organization?
— Amazon.com’s Jeff Bezos, in a 2016 CEO letter to shareholders

If you’re looking for a model of a big company that retains the dynamism of a startup, Amazon.com is a good place to start. Why? In part because, as the quote above suggests, founder and CEO Jeff Bezos knows that successful companies must nourish and retain one characteristic above all: vitality. At BCG, we define vitality as the capacity of a company to explore new options, renew its strategy, and grow sustainably. Preserving past advantages and position is not sufficient to thrive in today’s complex and dynamic business environment. In a fast-changing world, only the vital will survive.

Declining vitality is making large companies increasingly vulnerable to change, according to our research. A 2015 BCG study, for example, found that just 7% of companies that are market share leaders in their industries are also profit leaders. Many are merely hanging on. Loss of vitality stems in part from the natural life cycle of companies: The high growth rates typical of younger companies are hard to sustain. But in the long run, the majority of returns for shareholders are driven by revenue growth. For companies to prosper and deliver for investors well past the startup stage, they must learn the secrets of staying vital.

A forward-looking measure

Today, most business decisions are still informed using backward-looking financial metrics, with the implicit assumption that past success is predictive of future success. But the high rate of change and uncertainty driven by technology, business model innovation, and other factors make this assumption increasingly untenable and demand new metrics and approaches. We believe the Fortune Future index, based on the idea of vitality, can help fill this gap.

The result of a two-year research effort, the Future 50 ranks U.S.-listed companies with the best prospects for growth. The index has two pillars: 1) a market view of growth potential and 2) an assessment of the firm’s actual capacity to deliver that growth, based on four dimensions: strategy, technology and investments, people, and structure (click here for more on methodology). The result is a composite score that represents both a new metric and new perspective for business analysis.