Chemokines are a superfamily of small proteins that bind to G protein-coupled receptors on target cells and were originally discovered as mediators of directional migration of immune cells to sites of inflammation and injury. In recent years, it has become clear that the function of chemokines extends well beyond the role in leukocyte chemotaxis. They participate in organ development, angiogenesis/angiostasis, leukocyte trafficking and homing, tumorigenesis and metastasis, as well as in immune responses to microbial infection. Therefore, chemokines and their receptors are important targets for modulation of host responses in pathophysiological conditions and for therapeutic intervention of human diseases.