M-CSF (Macrophage colony-stimulating factor) is a potent lineage restricted haematopoietic growth factor and member of the CSF family of hormone-like glycoproteins, which plays a key role in the regulation of cellular differentiation, proliferation, and the survival of blood monocytes, tissue macrophages and their progenitor cells.

Along with sRANKL/CD254/OPGL, M-CSF is essential for osteoclastogenesis, acting through the tyrosine kinase receptor c-fms (colony stimulating factor 1 receptor). A genetic defect in M-CSF is responsible for osteopetrosis in mice (op/op), which are severely deficient in mature macrophages and have a restricted capacity for bone remodelling.