Three members of the Tec family kinases, Itk, Rlk and Tec, have been implicated in signaling downstream of the T cell receptor (TCR). The activity of these kinases in T cells has been shown to be important for the full activation of phospholipase C‐γ1 (PLC‐γ1). Disruption of Tec family signaling in Itk^–/– and Rlk^–/–Itk^–/– mice has multiple effects on T cell development, cytokine production and T‐helper cell differentiation. Furthermore, mice possessing mutations in signaling molecules upstream of PLC‐γ1, such as Src homology 2 (SH2) domain‐containing phosphoprotein of 76 kDa (SLP‐76), linker for activation of T cells (LAT) and Vav1, or in members of the nuclear factor for activated T cells (NFAT) family of transcription factors, which are downstream of PLC‐γ1, have been found to have similar phenotypes to Tec family‐deficient mice, emphasizing the importance of this pathway in regulating T cell activation, differentiation and homeostasis.