The stem cell factor receptor (SCFR) is a member of the receptor tyrosine kinase superfamily. It is expressed on a variety of cell types, including hematopoietic cells, germ cells, neural cells, melanocytes, and the interstitial cells of Cajal in the intestine. The absence of functional murine SCFR is lethal in utero. Mutations resulting in reduced expression, or function, of the SCFR lead to abnormalities in hematopoiesis, pigmentation, and reproduction in mice. Inappropriate expression or activation of the SCFR is associated with a variety of diseases, including mastocytosis in humans. Further, downregulation of the SCFR may play a role in metastatic melanoma. The importance of the SCFR in both normal and pathophysiology has led to extensive study of its mechanism of action. Recent work indicates that the SCFR activates multiple signal transduction pathways, including the Ras/ Raf MAP kinase cascade, the JAK/STAT pathway, phosphatidylinositol 3-kinase, and Src family members. This review will provide an overview of the structure, biology, and mechanism of action of the SCFR.