Interleukin-11 (IL-11) is an IL-6-type cytokine that is produced by a variety of stromal cells including fibroblasts, epithelial cells and osteoblasts. It binds to a multimeric receptor complex which contains an IL-11-specific α subunit and a promiscuous 130 kDa β subunit (gp130). IL-11 stimulates multiple aspects of hematopoiesis and hepatocyte production of acute phase response proteins. It also inhibits the genesis of adipocytes, activates osteoclasts, alters neural phenotype, stimulates tissue fibrosis and regulates chondrocyte, synoviocyte and B cell function. In other settings, IL-11 minimizes tissue injury. This may be the result of its ability to protect clonogenic stem cells, regulate epithelial cell proliferation, inhibit apoptosis and inhibit macrophage cytokine production. Thus, IL-11 appears to play an important role in hematopoiesis, bone metabolism and tissue remodeling and may be an important protector of mucosal surfaces.