Health investors may be venture capitalists, willing to take big risks for the possibility of big returns; foundations that use program-related investments to generate a return on capital while supporting their charitable interests; or social entrepreneurs, who hope to do well by doing good. The health investment space is huge — a Google search for the phrase “investing in health care” turns up almost half-a-million responses — but it is also uncertain. What can we learn about the future of health care from the people who are putting money into it? What’s the potential payoff, whether in profits or a healthier world?