This defining and original book explores the history of monopoly power and of its relation to competition, focusing on the innovative contributions of the Italian Marginalists - Pareto, Pantaleoni, De Viti de Marco and Barone. Manuela Mosca analyses their articulate vision of competition, and the structural and strategic entry barriers considered in their works to enrich existing literature on the history of the sources of market power. The book is not limited to the reconstruction of the elaboration of pure theory, it also highlights its policy implications and how this group applied their theories as cutting-edge experiments in analysing the labour market, socialism, the Great War and gender issues, against the background of the political situation of the period. Monopoly Power and Competition is a vital resource for historians of economic thought, as it explores a relatively untouched area of microeconomics in historical perspective, and reveals the theories surrounding monopoly power and competition. Microeconomists and industrial organisation scholars would similarly benefit from the knowledge of the origins of many microeconomic tools and notions.