The story of a bold political experiment in nineteenth-century France to establish power through finance. Amid the rise of industrial capitalism and revolutionary upheaval, French reformers asserted that finance should be reimagined as an instrument of economic and social transformation rather than left to the logic of private profit and speculation. In the 1850s, under Napoleon III's authoritarian regime, this vision took institutional form as the Bonapartist state strategically deployed finance, broadened market participation, and sponsored new banks with the promise of directing investment toward infrastructure and industry. Yet this effort to harness and mobilize capital ran into a problem: The financial markets refused to be tamed. Drawing on rich archival sources--from police surveillance and courtroom transcripts to investment manuals and petitions for incorporation-- Capital Untamed reveals how the financial markets became an instrument of political power, frustrated state ambitions, and ultimately escaped attempts at mastery. In this striking debut, historian Charlotte Robertson shows how the French state and its citizens navigated a turbulent era of European capitalism animated by debates over the social purpose of financial capital. Ultimately, politicians' efforts to establish legitimacy by reorganizing finance--and their confrontations with the limits of that project--set the stage for a form of modern discontent with the financial system that survives to this day.