Chemokines regulate T cell trafficking into secondary lymphoid organs and migration across endothelial cells in response to inflammatory signals. The small guanosine triphosphatase Rap1 is a critical regulator of chemokine signaling in T cells, but how chemokines activate Rap1 has been unclear. A study showed that Abl family tyrosine kinases were essential for chemokine-induced Rap1 activation, T cell polarization, and migration. Abl family kinases promoted Rap1 activation by phosphorylating the adaptor protein human enhancer of filamentation 1 (HEF1), thus establishing a critical Abl-HEF1-Rap1 signaling axis for chemokine-induced T cell migration.