Political Parties: A Sociological Study of the Oligarchical Tendencies of Modern Democracy is a book by sociologist Robert Michels, published in 1911 and first introducing the concept of iron law of oligarchy. It is considered one of the classics of social sciences, in particular sociology and political science. It was translated to Italian as Sociologia del partito politico nella democrazia moderna: studi sulle tendenze oligarchiche degli aggregati politici by Alfredo Polledro in 1912, and then translated from the Italian to English by Eden Paul and Cedar Paul for Hearst's International Library Co. in 1915.