This report from a recent meeting* highlights some of the key developments in eosinophil research and assesses their impact on current views of the role of eosinophils in inflammation. Considerable progress has been made in defining the structure, constituents and properties of eosinophils in vitro and these new insights into eosinophil biology are summarized. A new era is beginning in which the roles of eosinophils can be assessed and defined in vivo.