The Tec kinases represent the second largest family of mammalian non-receptor tyrosine kinases and are distinguished by the presence of distinct proline-rich regions and pleckstrin homology domains that are required for proper regulation and activation. Best studied in lymphocyte and mast cells, these kinases are critical for the full activation of phospholipase-C gamma (PLC-gamma) and Ca(2+) mobilization downstream of antigen receptors. However, it has become increasingly clear that these kinases are activated downstream of many cell-surface receptors, including receptor tyrosine kinases, cytokine receptors, integrins and G-protein-coupled receptors. Evidence suggests that the Tec kinases influence a wide range of signaling pathways controlling activation of MAP kinases, actin reorganization, transcriptional regulation, cell survival and cellular transformation. Their impact on cellular physiology suggests that the Tec kinases help regulate multiple cellular processes beyond Ca(2+) mobilization.