Political Parties: A Sociological Study of the Oligarchical Tendencies of Modern Democracy (German: Zur Soziologie des Parteiwesens in der modernen Demokratie; Untersuchungen über die oligarchischen Tendenzen des Gruppenlebens) is a book by the German-born Italian sociologist Robert Michels, published in 1911 and first introducing the concept of iron law of oligarchy.

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.

[4] Such social systems have to be organized along bureaucratic lines, managed by departments staffed with non-elected officials,[5] and bureaucracies inevitably develop oligarchies.

[6] Such leaders will amass resources (superior knowledge control over the formal means of communication with the membership, and the skill in the art of politics) giving them power at the expense of rank and file members.

[6] "Large-scale organizations give their officers a near monopoly of power"Second, Michels expressed doubts about whether the rank and file possess the skills necessary to compete with the leaders, a concept he phrased as the "incompetence of the masses".

"[12] Michels work significantly influenced the views on political party theory by his friend and one of the founding fathers of sociology, Max Weber.