B-cell activating factor (BAFF), also known as B lymphocyte stimulator (BLyS), is a cytokine that belongs to the tumor necrosis factor (TNF) ligand superfamily and plays a crucial role in regulating B-cell development, survival, and function. In humans, BAFF is primarily produced by myeloid cells, including monocytes, macrophages, and dendritic cells, and acts on B cells through binding to its receptors, BAFF-R, TACI, and BCMA. By engaging these receptors, BAFF promotes the survival, maturation, and antibody production of B cells, as well as the formation of germinal centers and the maintenance of peripheral B-cell populations. Dysregulation of BAFF signaling has been implicated in various autoimmune diseases, such as systemic lupus erythematosus (SLE) and rheumatoid arthritis, highlighting the importance of BAFF in immune homeostasis and autoimmunity.