This book examines the long, complicated and turbulent history of the EU Emissions Trading System (ETS), widely regarded as a cornerstone of EU climate and energy policy. Ten key lessons from the functioning of the system are identified, including the importance of historical and contextual conditions for understanding design choices and results over time. The book also looks ahead and discusses whether the ETS can continue to operate to achieve the EU's long-term net-zero ambitions. Central EU-internal and external challenges are also discussed, including the rise of populism and geopolitical turbulence. The book will appeal to all those interested in climate and energy policy, carbon market politics, European politics, and populism studies.