Chemokines facilitate leukocyte migration and positioning as well as other processes such as angiogenesis and leukocyte degranulation. The burgeoning knowledge on chemokines and their receptors has influenced many aspects of immunology, in part because cell migration is intimately related to leukocyte function. This overview assesses the impact that chemokines have had on our understanding of immunology and infectious diseases. These include the role of chemokines in leukocyte-endothelial cell interactions; dendritic cell function; T cell differentiation and function; inflammatory diseases; mucosal and subcutaneous immunity; and subversion of immune responses by viruses, including HIV-1. This knowledge heralds new opportunities for the manipulation of immune responses and the development of new anti-inflammatory therapies. It has also provided a new perspective on the functioning of the immune system.