Green growth promises to transform climate change mitigation from a problem to an economic sure thing. By making investment in energy efficiency and low-emissions energy the foundation of a new industrial revolution, green growth promises to relieve the intractable conflict between high-carbon losers and low-carbon winners. This book addresses the challenges and opportunities for green growth. Advocates for green growth have yet to show how investments in emissions reduction translate into improvements in economic productivity. As the first half of this book illustrates, most green growth successes so far face limits to their ability to generate sustained economic improvement. We propose that real green growth must focus on how a low-carbon energy systems transformation will create growth in the broader economy. Previous transformations, in coal, oil, or electricity, drove growth primarily via the new kinds of production they made possible in the economy writ large. Whether low-carbon energy may do the same remains unclear. The second half addresses how we might discover these transformative gains. We introduce the idea of a “green spiral”, in which early policy action creates supportive constituencies with an economic stake in further progress towards a low-emissions energy system. Country case studies illustrate the potential for this feedback loop to operate in different national contexts. With this action occurring despite little progress on a global climate deal, we conclude that an international climate change treaty may be the product, not the start, of effective national action on emissions reduction.