The iron law of oligarchy is a political theory, first developed by the German syndicalist sociologist Robert Michels in his 1911 book, Political Parties.

The “iron law of oligarchy” states that all forms of organization, regardless of how democratic or autocratic they may be at the start, will eventually and inevitably develop oligarchic tendencies, thus making true democracy practically and theoretically impossible, especially in large groups and complex organizations. The relative structural fluidity in a small-scale democracy succumbs to “social viscosity” in a large-scale organization. According to the “iron law,” democracy and large-scale organization are incompatible.