Book excerpt: Can the power of the G20 be legitimate? This book examines the politics surrounding the G20’s efforts to act effectively and legitimately and the problems and challenges involved in this activity. Developing a critical constructivist conceptualisation of the G20, the book considers holistically and practically the ways that the G20 develops various forms of power and influence and acts as an apex form of global governance that seeks to be an overall coordinating forum to address global problems. Assessing how debates about the legitimacy of the G20 shaped its operation, Slaughter argues that the G20’s power can be legitimate despite a range of considerable challenges and limits. The book also explores what measures the G20 could take to be more legitimate in the future. Offering a direct and accessible consideration of the politics of legitimacy with respect to the G20, this book will be of interest to those attempting to understand and analyse the G20 as well as to scholars of IR theory, global political economy, global policy, diplomacy and globalisation.