This book demonstrates the importance of Léon Duguit for property theory in both the civil and common law world. It translates into English for the first time ever Duguit's seminal lecture on property, the sixth of a series given in 1911 in Buenos Aires. It also collects essays from the leading experts on the social function of property in major civil and common law jurisdictions internationally. The book explores the importance that the notion of the social function of property has come to have not only in France but in the entire civil law tradition, and also considers the wide - if un-attributed and seldom regarded - influence in the common law tradition and theory of property.