The T cells scan the surface of antigen-presenting cells with their T cell receptors (TCR) in order to find and respond to specific peptide-major histocompatibility complexes (pMHC). Since mainly self-peptides are expressed on antigen-presenting cells, the T cells must utilize sensible mechanisms in order to quickly discriminate between self and nonself-peptides. A range of different models have been proposed to account for this process. Due to the experimental inconsistency of how T cells respond to altered peptides it has been difficult to validate the competing models. Recent models, based on the kinetic proofreading model, propose that a short life-time of the TCR/pMHC complexes may be compensated by fast rebinding of the individual molecules. Hence, both the on- and off-rate involved in the interaction between pMHCs and TCRs will determine the fate of the T cell discrimination. I here briefly review some of the proposed models on T cell discrimination and scanning, and discuss the significance of determining self-peptide kinetics to validate the different models.