**Bacillus Calmette-Guérin (BCG)** is a live attenuated bacterial preparation derived from *Mycobacterium bovis* and is mainly used as a vaccine for the prevention of **tuberculosis (TB)**, particularly severe forms of the disease in infants and children. It works by stimulating the body’s immune system to develop protection against tuberculosis infection. In addition to its role as a vaccine, BCG is also used in medical therapy for **non-muscle invasive bladder cancer**, where it activates the immune response within the bladder to help destroy cancer cells and reduce the risk of tumor recurrence.