Allergic asthma is a prototypic Th2 mediated disease, where chemokines orchestrate the inflammatory cell recruitment. Most chemokines have a pro-inflammatory role. In this review, we focus on the potential role, in asthma and lung immunity, of CCL18 a chemokine both constitutively expressed at high levels in the lung and induced in inflammatory conditions. This chemokine is mainly produced by antigen presenting cells, and induced by Th2 type cytokines. The available data suggest that this chemokine may exhibit dual functions, with both pro- and anti-inflammatory properties, the latter through its ability to generate adaptive regulatory T cells in healthy subjects, with a loss of function in allergic patients. However, the functional implications are at the moment hampered by the lack of data on the nature of its putative receptor, and the absence of murine orthologue.