Recruitment of leukocytes either during development or to the site of injury is crucial. The molecular regulation of cell trafficking is complex but well orchestrated by the temporal and spatial expression of a multitude of chemokines (chemoattractant cytokines) and chemokine receptors. The chemokines, classified primarily into four classes (CC, C, CXC and CX3C) bind either to specific or shared receptors and often exhibit intra-class redundancy. At the cellular level, the biological activity of chemokines is finely controlled by varied receptor display, binding affinity and/or varied signal-transducing mechanisms. Perturbation in these finely regulated processes leads to acute or chronic inflammatory conditions, developmental abnormalities and tumorigenesis/angiogenesis.