In Populism, Demagoguery, and Tyranny, Tomás Pacheco-Bethencourt examines the political challenges posed by populism to constitutional democracy, with a twofold aim of clarifying its impact and addressing it effectively. He combines conceptual history, history of political thought, political history, and political philosophy to help analyze the political impact of populism on constitutional democracies. Pacheco-Bethencourt begins his analysis by demonstrating that lessons can be learned by bringing ancient Greece’s institutional framework to the discussion. It was during this time that republican procedures and practices of constitutionalism were born, explored, and refined by new oversight strategies. To underpin the argument, Pacheco-Bethencourt dives into examples of populist movements in Argentina, Venezuela, Hungary, Poland, France, and Spain to establish how the theory and real politics meet. It is here that the connection between populist rhetoric and political opportunism is exemplified. Politicians use populism as a tool to strategically reach power or push their political agenda, bridging strategy and politics. Opportunism has an ethical dimension that has to do with self-serving actions and willingness to deceive, akin to what could be compared to the negative connotations of classical demagoguery, also explored herein. This book will be of great interest to researchers studying populism and its future in modern politics, in addition to undergraduate and postgraduate students of populist rhetoric.