Human Stem Cell Factor (SCF) (also known as KIT ligand, KITLG, mast cell growth factor, or steel factor) is a cytokine and growth factor that plays a central role in hematopoiesis, stem cell maintenance, and immune cell development. SCF belongs to a group of hematopoietic growth factors that regulate the survival, proliferation, and differentiation of stem and progenitor cells. It functions by binding to the c-Kit receptor (CD117), a receptor tyrosine kinase expressed on hematopoietic stem cells, mast cells, melanocytes, and germ cells, activating intracellular signaling pathways including PI3K/AKT, MAPK, and JAK/STAT that promote cell survival, proliferation, and differentiation. In humans, SCF is produced by bone marrow stromal cells, fibroblasts, endothelial cells, epithelial cells, and other supporting cells, and exists in both membrane-bound and soluble forms, allowing both local and systemic regulation of c-Kit–expressing cells. SCF is essential for hematopoietic stem cell maintenance within the bone marrow niche, as well as for mast cell development, melanocyte function, and germ cell survival. Dysregulation of SCF–c-Kit signaling has been implicated in several diseases, including mastocytosis, gastrointestinal stromal tumors (GIST), melanoma, and certain leukemias, where abnormal activation of the c-Kit pathway can drive uncontrolled cell proliferation. Because of its critical role in stem cell biology, hematopoiesis, and oncogenic signaling, human SCF is widely studied in hematology, cancer biology, immunology, and regenerative medicine, contributing to development of therapies targeting the SCF–c-Kit signaling axis.