In many industries today, such as air travel, banking, internet search or social networking, there are only a few major competitors in any domestic market. Those large companies’ shares are often held by a few prominent investment companies like Blackrock, State Street, or Fidelity. Recent econometric research suggests that this market structure: oligopolistic industries owned by oligopolistic investors, leads to monopolistic behavior. What should we make of this econometric research? How has ownership of oligopolistic companies become so concentrated in the first place? And, what can we do about these modern monopolies?