The TEC-family protein tyrosine kinases ITK, RLK and TEC have been identified as key components of T-cell-receptor signalling that contribute to the regulation of phospholipase C-γ, the mobilization of Ca²⁺ and the activation of mitogen-activated protein kinases. Recent data also show that TEC kinases contribute to T-cell-receptor-driven actin reorganization and cell polarization, which are required for productive T-cell activation. Functional studies have implicated TEC kinases as important mediators of pathways that control the differentiation of CD4⁺ T helper cells. Here, we review studies of signalling pathways that involve TEC kinases and how these pathways might contribute to the regulation of T-helper-cell differentiation and function.