The mammary gland is prone to a wide variety of disorders that affect the quality and quantity of milk. The mammary gland disorders can be categorized into congenital disorders (supernumerary teats, nonfunctional quarters), physiological disorders (udder edema, precocious mammary development, failure of milk ejection, agalactia, galactorrhea), diseases of teats and skin (ulcerative mammillitis, fibropapillomas, hyperkeratosis at teat-end, necrotic dermatitis, udder impetigo, udder cleft dermatitis), and inflammatory (mastitis) and traumatic disorders (laceration of the bovine udder, teat obstructions, breakdown of udder support apparatus, hemolactia, teat sphincter inadequacy). The present chapter encompasses all these disorders, their predisposing factors, treatment, and prevention.