Why do some ideas make it big while others fail to take off? One of today's leading behavioral economists says it comes down to a single question: Can the idea scale? All great ideas have one thing in common: They are not guaranteed to succeed.Be it a medical breakthrough, a policy initiative, a product innovation or a social movement, translating an idea into widespread impact depends on one thing only: whether it can be replicated at scale."Scale" has become a favored buzzword in the startup world. But scale isn't just about accumulating more users or capturing more market share. It's about whether an idea that takes hold in a small group can do the same in a much larger one. Scalability is critical to everything from expanding a small business, to narrowing the national achievement gap, to delivering billions of doses of a vaccine, to making a new technology widely affordable - and much more.While all successfully scaled ideas are alike, all unscalable ideas fail in their own way. To succeed, says University of Chicago economist John A. List, an idea must achieve "high voltage": a set of characteristics that predict its ability to scale. Drawing on his own original research-as well as fascinating examples from the realms of business, government, education, and public health-List offers proven strategies for avoiding voltage drops, and engineering voltage gains, including how to: • Ensure that your early success is not a false positive. • Determine if your initial audience is representative of the larger population • Use behavioral economic incentives to spur wider adoption of your idea • Ensure viability at scale by getting the most out of every last dollar you spend By understanding the science of scaling, we can drive change in our schools, workplaces, communities, and society at large. Because a better world can only be built at scale.