Chemokines represent key factors in the outburst of the immune response, by activating and directing the leukocyte traffic, both in lymphopoiesis and in immune surveillance. Neurobiologists took little interest in chemokines for many years, until their link to acquired immune deficiency syndromeassociated dementia became established, and thus their importance in this field has been neglected. Nevertheless, the body of data on their expression and role in the CNS has grown in the past few years, along with a new vision of brain as an immunologically competent and active organ. A large number of chemokines and chemokine receptors are expressed in neurons, astrocytes, microglia and oligodendrocytes, either constitutively or induced by inflammatory mediators. They are involved in many neuropathological processes in which an inflammatory state persists, as well as in brain tumor progression and metastasis. Moreover, there is evidence for a crucial role of CNS chemokines under physiological conditions, similar to well known functions in the immune system, such as proliferation and developmental patterning, but also peculiar to the CNS, such as regulation of neural transmission, plasticity and survival. Keywords: acquired immune deficiency syndrome dementia complex, Alzheimer's disease, brain tumors, chemokines, multiple sclerosis, stroke. Since their discovery in 1987, when a new factor with chemotactic activity for neutrophils (later named interleukin IL 8, now called CXCL8) was identified, the chemokine family has grown and more than 50 chemokines that interact with at least 20 receptors have been identified to date (Walz et al. 1987;Yoshimura et al. 1987). Chemokines are a group of structurally and functionally related proteins that exert their biological activity by binding to cell surface receptors in many instances through interaction with sulfated proteins and proteoglycans. Chemokines have been highly conserved during evolution, as indicated by their expression in numerous different species of mammals, birds and fish, and by the amino acid similarities across species. These proteins are produced by many cellular sources and their actions cover a wide range of functions.Chemokines were initially recognized to play a role in leukocyte communication and migration, both in physiological and pathological contexts. These molecules control immune cell trafficking and recirculation of the leukocyte population between the blood vessels, lymph, lymphoid organs and tissues, a process important in host immune