Fractalkine has been recognized as the first member of the fourth chemokine family recently and its receptor, CX3CR1, was identified afterwards. This pair of ligand/receptor play important roles in the migration and adhesion of peripheral leukocyte through different ways. They are also likely to be related to the embryogenesis and regeneration of several organs and may possess some functions in the central nervous system. Fractalkine has been recognized as the first member of the fourth chemokine family recently and its receptor, CX3CR1, was identified afterwards. These pair of ligand / receptor play important roles in the migration and adhesion of peripheral leukocyte through different ways. They are also likely to be related to the embryogenesis and regeneration of several organs and may possess some functions in the central nervous system.