Chemokines and their receptors have long been recognized as key molecules directing leukocyte migration between blood, lymph and tissues. Evidence accumulated in recent years indicates that, in addition to their chemotactic functions, chemokine receptors are highly versatile players fine-tuning immune responses. Chemokine receptors and ligands have been implicated in dendritic-cell maturation, signal transmission at the immunological synapse between T lymphocytes and their cellular partners, and in the polarization of immune responses. These findings identify new roles for chemokines in T-cell triggering and activation of effector functions, and suggest that these small cytokines represent key conductors of adaptive immunity.