BAFF (B-cell activating factor), also known as BLyS (B lymphocyte stimulator), is a cytokine that plays a critical role in the survival, activation, and differentiation of B cells. It is primarily produced by monocytes, dendritic cells, and stromal cells. BAFF is essential for maintaining the homeostasis of the B cell population, promoting B cell survival and maturation, and supporting the development of humoral immunity. By interacting with its receptors (BAFF-R, TACI, and BCMA) on B cells, BAFF regulates key processes such as B cell proliferation, class switching, and antibody production. Due to its importance in B cell function, BAFF is implicated in autoimmune diseases like systemic lupus erythematosus (SLE) and other B cell-driven pathologies.