In Monopoly Politics, Erik Peinert provides a macro-historical explanation for why American and international markets are today monopolized by an ever-narrowing group of companies. Using original archival evidence from the United States and France, and borrowing insights from microeconomics, bureaucratic politics, sociology, psychology, and law, Peinert demonstrates how government policy towards competition and monopoly changes at key moments in the 20th century. Centrally, policy changes as a result of the interaction between staff turnover in policy circles and the diminishing returns to policy regimes.As policy regimes across different arenas such as antitrust, intellectual property, trade, and industrial policy push consistently either in favor of competition or monopoly, they generate diminishing returns. Unsustainably pushing for competition suppresses profits and destabilizes markets, whereas pushing to defend market power will raise prices, stifle innovation, and concentrate profits in stagnant monopolies. However, with policy regimes locked in by committed policymakers who have invested time, reputation, or the careers into implementing one approach to policy, government policy only changes through their replacement with non-committed officials willing to reconsider policy. Examining policy change in the United States and France over the 20th century, and leveraging tens of thousands of archival documents, Peinert traces new policy ideas or frameworks through each government, from the site of the original insight to final decision-making, showing the economic research, theories, and interests that motivated the policy discussions "in the room," and the key considerations influencing final policy choices.