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Eosinophils are heavily elevated during helminth infections and a range of allergic and inflammatory disorders, but are also present in several tissues in the absence of infection. Indeed, new findings demonstrate that eosinophils may be involved in events as diverse as glucose metabolism, mammary gland development, intestinal health, tissue remodelling, thymic selection and B-cell survival. Although eosinophils often correlate with pathological parameters during conditions such as inflammatory bowel disease and asthma, the evidence for their contribution to tissue pathology remains controversial. Recent research suggests that eosinophils may have additional roles in these settings, related to control and resolution of inflammation. Controversy also surrounds the involvement of eosinophils in anti-helminth immunity. Their assumed role in fighting parasites has increasingly come into question, in particular by data from eosinophil ablated mouse strains in which either no or only very moderate effects on helminth survival has been reported. Helminths are masters of immune regulation, but whether they actively suppress eosinophil function has rarely been considered. Thus, the purpose of this review is threefold; 1) To summarize our knowledge of the wide range of functions of eosinophils during homeostasis. 2) To discuss the role of eosinophil during inflammation and the recent discovery of eosinophils as mediators of inflammatory resolution. 3) To summarize data on the effect of eosinophils on helminth infections and discuss the possibility of helminth-mediated modulation of eosinophils.