Drosophila haemopoiesis gives rise to three independent cell lineages: plasmatocytes, crystal cells and lamellocytes. The regulation of Drosophila stem cell proliferation and lineage specification involves transactivators and signalling pathways, many of which have mammalian counterparts that control haemopoietic processes. Drosophila plasmatocytes are professional phagocytes that resemble the monocyte/macrophage lineage, crystal cells play a critical role in defence-related melanisation, and lamellocytes encapsulate large invaders. Crystal cells and lamellocytes have no clear mammalian homologues. Research into the molecular mechanisms that underlie the various immune functions of Drosophila blood cells, such as non-self recognition, is now taking wing.