What can Procter & Gamble learn from Method, the San Francisco purveyor of natural home products? How about Fidelity Investments — could it profit from observing Zurich’s Sustainable Asset Management? What lessons are offered to mainstream companies by mission-driven companies, those small- and medium-sized enterprises that balance profitability with social and environmental goals? By studying them, mainstream companies can get beyond the fruitless debate over whether it pays to be responsible, and move onto a far more important issue: How they can make being responsible pay.