Heart transplant rejection has sharply declined with the introduction of effective immunosuppression, including calcineurin inhibitors. Improvement in survival rates has permitted cardiac transplantation to become, arguably, the most durable option for end-stage heart disease. The risk of rejection persists significantly, particularly in the early period following transplantation, and if untreated, is associated with poor clinical outcomes. Therefore, routine surveillance for both acute cellular rejection and antibody-mediated rejection is critical. This chapter will discuss forms of surveillance for cardiac allograft rejection, including standard and emerging diagnostic methods.