Impact investing has captured the world’s imagination. Just six years after the Rockefeller Foundation coined the term, the sector is booming. An estimated 250 funds are actively raising capital in a market that the Global Impact Investing Network estimates at $25 billion. Giving Pledge members described impact investing as the “hottest topic” at their May 2012 meeting, and Prime Minister David Cameron extolled the potential of the sector at the most recent G8 summit.  Sir Ronald Cohen and HBS Professor William A. Sahlman describe impact investing as the new venture capital, implying that it will, in the next 5 to 10 years, make its way into mainstream financial portfolios, unlocking billions or trillions of dollars in new capital.