In this publication we teamed up with our collaborators from Thailand to write a review on the role of the WASp protein in T cell activation. WASp is an important actin nucleation factor in immune cells that is recruited to TCR microclusters, where it is activated and regulates actin network formation. In the review we highlight the findings on WASp-deficient T cells from both human and mice in TCR-mediated signal transduction. We discuss the role of WASp in proximal TCR signaling as well as in the MAPK, PKC and Ca pathways.