Chemokines are small proteins that can act on cells that express matching receptors. They are best known for their role in migration of cells, especially immune cells. Chemokine/chemokine-receptor pairs are often functionally categorized into three groups: inflammatory, homeostatic, and angiogenic/angiostatic, although functions sometimes overlap. Interfering with the interaction between chemokines and their receptors is currently under investigation as a therapeutic strategy in rheumatoid arthritis.