T-cell recognition of allopeptides presented either by recipient or donor major histocompatibility complex molecules represents a key component for the initiation of T-cell responses to alloantigens. However, the mechanisms by which this presentation occurs continue to be a source of debate and have received considerable attention in the literature over the past few years. Better understanding of the mechanisms of allorecognition is essential for the future development of specific immunotherapies and novel approaches for the induction of transplantation tolerance. This article reviews recent publications that represent advances made in our understanding of T-cell allorecognition and its role in allograft rejection.