In the late 1990s, a small group of policy entrepreneurs snuck a modest provision into a larger electricity-restructuring bill passing through the Massachusetts legislature. It was so obscure that the media scarcely noticed it — it's not even clear if the governor's staff knew it was in there. The policy had a different name then, but today it's come to be known as "community choice aggregation." The idea is simple: communities can band together and take over energy procurement from their electrical utilities. The utilities remain responsible for infrastructure and billing, but the communities get to decide where their energy comes from and what kind of energy it is. Since that humble beginning, community choice aggregation has taken off. Currently more than 1,800 communities in six states, comprising 36 million customers (some 11 percent of US ratepayers), choose their own energy supply. There are more states and communities considering community choice aggregation every day. It is, in our otherwise grim times, a hopeful story about climate policy — a true demonstration of the power of grassroots activism to make lasting change. David Hsu, an associate professor of urban and environmental planning at MIT, has researched the origins and growth of community choice aggregation and recently published the results in the journal Energy Research & Social Science. I thought I would have him on the pod to talk about how this unassuming policy with the difficult-to-remember name grew from such modest beginnings to such sprawling size, so fast. We also discussed the differences among different community choice aggregations, the kinds of innovations they are spawning, and their future trajectory. Get full access to Volts at www.volts.wtf/subscribe