Fusion energy is a radical innovation: a transformative solution to future energy needs. Its development blends curiosity-driven science with practical goals. Fusion’s progress fits key innovation concepts, including: Projects such as ITER and STEP face typical “mega project” challenges: high costs, delays, and uncertainty, but also serve as platforms for learning-by-doing and innovation. Fusion’s story includes episodes of failure, chance, and serendipity, reminding us that innovation is as much about people and learning as it is about science and technology. Fusion research has seen many costly failures, including abandoned or over-budget projects, but these have all in their way contributed to progress.