This updated edition delves into the intricate challenges of high-energy confinement in tokamaks and stellarators, exploring phenomena like mode avalanches, chirping, and particle resonances. Building on foundational principles, the book examines unexpected insights into magnetic and orbit helicity, particularly for fusion-produced alpha particles. Addressing the urgent need for CO2-free energy, it also highlights advancements in reactor design and the technical hurdles still facing commercially viable fusion power. Aimed at both students and researchers, this volume offers deep scientific insights, supported by contributions from leading global experts in the field.