The T-cell receptor (TCR) is critical for T-cell lineage selection, antigen specificity, effector function and survival. Recently, TCR gene transfer has been developed as a reliable method to generate ex vivo large numbers of T cells of a given antigen-specificity and functional avidity. Such approaches have major applications for the adoptive cellular therapy of viral infectious diseases, virus-associated malignancies and cancer. TCR gene transfer utilizes retroviral or lentiviral constructs containing the gene sequences of the TCR-alpha and TCR-beta chains, which have been cloned from a clonal T-cell population of the desired antigen specificity. The TCR-encoding vector is then used to infect (transduce) primary T cells in vitro. To generate a transduced T cell with the desired functional specificity, the introduced TCR-alpha and TCR-beta chains must form a heterodimer and associate with the CD3 complex in order to be stably expressed at the T-cell surface. In order to optimize the function of TCR-transduced T cells, researchers in the field of TCR gene transfer have exploited many aspects of basic research in T-cell immunology relating to TCR structure, TCR-CD3 assembly, cell-surface TCR expression, TCR-peptide/major histocompatibility complex (MHC) affinity and TCR signalling. However, improving the introduction of exogenous TCRs into naturally occurring T cells has provided further insights into basic T-cell immunology. The aim of this review was to discuss the molecular immunology lessons learnt through therapeutic TCR transfer.