Follitropin Subunit β (FSHB) is a secreted protein that belongs to the glycoprotein hormones subunit β family. The pituitary glycoprotein hormone family includes follicle-stimulating hormone, luteinizing hormone, chorionic gonadotropin, and thyroid-stimulating hormone. FSHB exists in a heterodimer of a common α chain and an unique β chain that confers biological specificity to thyrotropin, lutropin, follitropin, and gonadotropin. FSHB stimulates development of follicle and spermatogenesis in the reproductive organs. Defects in FSHB are a cause of isolated follicle-stimulating hormone deficiency (IFSHD).