Cytoplasmic protein‐tyrosine kinases (PTKs) are enzymes involved in transducing a vast number of signals in metazoans. The importance of the Tec family of kinases was immediately recognized when, in 1993, mutations in the gene encoding Bruton's tyrosine kinase (Btk) were reported to cause the human disease X‐linked agammaglobulinemia (XLA).(1,2) Since then, additional kinases belonging to this family have been isolated, and the availability of full genome sequences allows identification of all members in selected species enabling phylogenetic considerations. Tec kinases are endowed with Pleckstrin homology (PH) and Tec homology (TH) domains and are involved in diverse biological processes related to the control of survival and differentiation fate. Membrane translocation resulting in the activation of Tec kinases with subsequent Ca²⁺ release seems to be a general feature. However, nuclear translocation may also be of importance. The purpose of this essay is to characterize members of the Tec family and discuss their involvement in signaling. The three‐dimensional structure, expression pattern and evolutionary aspects will also be considered. BioEssays 23:436–446, 2001. © 2001 John Wiley & Sons, Inc.