This is a book by the 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.

This work analyses the power structures of organizations such as political parties and trade unions. Michels's main argument is that all organizations, even those in theory most egalitarian and most committed to democracy – like socialist political parties – are in fact oligarchical, and dominated by a small group of leadership. The book also provides a first systematic analysis of how a radical political party loses its radical goals under the dynamics of electoral participation. The origins of moderation theory can be found in this analysis.

(This is a translation. Book was first published in German under the title Zur Soziologie des Parteiwesens in der modernen Demokratie; Untersuchungen über die oligarchischen Tendenzen des Gruppenlebens.)