T cell recognition of specific antigens mediates protection from pathogens and controls neoplasias， but can also cause autoimmunity. Our knowledge of T?cell antigens and their implications for human health is limited by the technical limitations of T?cell profiling technologies. Here， we present T-Scan， a high-throughput platform for identification of antigens productively recognized by T?cells. T-Scan uses lentiviral delivery of antigen libraries into cells for endogenous processing and presentation on major histocompatibility complex (MHC) molecules. Target cells functionally recognized by T?cells are isolated using a reporter for granzyme B activity， and the antigens mediating recognition are identified by next-generation sequencing. We show T-Scan correctly identifies cognate antigens of T?cell receptors (TCRs) from viral and human genome-wide libraries. We apply T-Scan to discover new viral antigens， perform high-resolution mapping of TCR specificity， and characterize the reactivity of a tumor-derived TCR. T-Scan is a powerful approach for studying T?cell responses.