In this paper, I identify the bottom of the pyramid (BOP) markets as a new source of radical innovation. By focusing managerial attention on creating awareness, access, affordability, and availability (4As), managers can create an exciting environment for innovation. I suggest that external constraints can be utilized to build an innovation sandbox within which new products and business models can be created. Using a live example of such an innovation—the development of the biomass stove for the rural poor in India—I illustrate the process and the usefulness of the approach. Increasingly, global firms are recognizing the implications of innovations at the BOP for developed markets as well.