Vertical restraints imposed on some downstream buyers can affect non-contracted firms by weakening upstream suppliers’ effective viability. We study these contracting externalities using Intel’s exclusionary agreements with PC manufacturers in the microprocessor market. Combining litigation-based measures of restraints with PC data, we estimate dynamic models of AMD adoption that allow for cross-buyer spillovers. We find that exclusivity imposed on a given buyer significantly reduces adoption by other, non-contracted buyers, generating sizable and persistent market-wide effects. The paper provides the first empirical quantification of the economic magnitude of contracting externalities and highlights the broader competitive risks posed by exclusionary contracting.