In his historic 1919 dissent, Justice Oliver Wendell Holmes named, and thus catalyzed the creation of, the marketplace of ideas. This conceptual space has, ever since, been used to give shape to American constitutional notions of the freedom of expression. It has also eluded clear definition, as jurists and scholars have contested its meaning for more than a century. In The Structure of Ideas, Jared Schroeder takes on the task of mapping the various iterations of the marketplace, from its early foundations in Enlightenment beliefs in universal truths and rational actors, to its increasingly expansive parameters for protecting expression in the arenas of commercial, corporate, and online speech. Schroeder contends that in today''s information landscape, marked by the rapid emergence of artificial intelligence, the marketplace is failing to provide a space where truths succeed and falsity fails. AI and networked technologies have thoroughly overpowered all traditional pictures of the marketplace up to now. Schroeder proposes various theoretical interventions that would revise the marketplace for the current moment, and concludes by describing a new space built around algorithms, AI, and virtual communication.