Gregory F. Nemet examines how solar photovoltaic technology became cheap enough to compete with fossil fuels, tracing the contributions of governments, firms, and researchers across the United States, Japan, Germany, Australia, and China. The dramatic decline in solar costs, by over 99 percent since the 1970s, represents one of the most successful examples of innovation policy, but its lessons are often misunderstood. Nemet shows that the process required sustained public investment over decades, not just initial research but also deployment policies that created markets allowing manufacturers to learn by doing. He traces how different countries contributed different elements: American research on fundamental science, Japanese manufacturing innovations, German deployment subsidies that created volume, and Chinese scaling that drove final cost reductions. The book examines which policy interventions were most effective and which wasted resources, providing lessons for accelerating other technologies needed for climate mitigation. Nemet challenges simple narratives about solar's success while affirming that intentional policy choices made the difference. The analysis shows how technological innovation actually works, through complex interactions between research, markets, and policy, rather than the romantic stories of lone inventors or the invisible hand of markets.