Oncostatin M (OSM) is a cytokine that is produced by macrophages, dendritic cells, and T lymphocytes during inflammatory events. The Type-I and Type-II OSM receptors are located on the cell surface of endothelial and tumor cells, contain the glycoprotein 130 (gp130) subunit, and activate the JAK/STAT signaling pathway. OSM functions to inhibit tumor cell proliferation, induce liver stem cell maturation, regulate cytokine production during hematopoiesis and inflammation, stimulate bone formation, and promote nervous system development.