Phagocytes are the founding pillars of innate immunity [1] and, as such, have been the object of intense scrutiny in the past few years. Mononuclear phagocytes constitute a system characterised by considerable diversity. Indeed, two major themes have emerged in recent macrophage investigations: their heterogeneity in different tissue environments and phenotypic plasticity in various physiologic and pathologic states [2–5]. Macrophages contribute to tissue homeostasis by the clearance of effete and injured host components and to defence against infection by phagocytosis and microbial killing. Their secretory activities are central to inflammation and its resolution; and it has been widely recognised that they are prominent in modified forms of inflammation such as atherosclerosis and cancer. Yet, many questions remain regarding the molecular basis of their role in pathogenesis and the identification of potential targets for therapeutic manipulation. The Viewpoints in this issue of the journal provide an overview of some of the central themes in macrophage research.