It's beginning to feel like a new feature of the business cycle: Every few years or so, American companies and consumers embrace the concept of green business. We're certainly in the midst of one of those moments right now. But something seems different about our current green awakening.

This time, the action is being driven as much by markets as morality. High oil prices, global warming, the sense that chemicals cause real harm and the earth's resources are indeed finite--these are not so much charitable causes to embrace as they are problems that entrepreneurs can solve. Wall Street and Silicon Valley certainly understand this: Venture capital firms invested $958 million in renewable energy companies in the first half of 2006 alone.

Today's green revolution is being driven by a whole new set of entrepreneurs. We asked our staffers and contributors to find the most intriguing ones out there; then we narrowed the list to the 50 in the pages that follow--The Green 50. The range of businesses is astonishingly wide, from high-tech firms making big bets on the future of energy to decidedly low-tech concerns that are simply determined to find a different way to do business. What their efforts add up to is a new way to think about being in business. We're betting that most of them will be around for several business cycles to come.

The Green 50 profiles were written by Martha Baer, Adam Bluestein, Max Chafkin, Jennifer Gill, Bobbie Gossage, Ryan McCarthy, Katharine Mieszkowski, Athena Schindelheim, Kasey Wehrum, and Alison Stein Wellner.