Bladder cancer is the second most common cancer of the urinary tract, and overall it is among the top 10 cancers in men. Transitional cell carcinoma (TCC) is the most common type, with the majority being superficial disease, i.e. the tumour has not gone beyond the lamina propria. The main problem with superficial TCC is the high recurrence rate. Various forms of treatment methods have been attempted to reduce the recurrence rate, with intravesical bacillus Calmette-Guerin (BCG) being the most successful to date. In fact, intravesical BCG is one of the most successful forms of immunotherapy in the treatment of any form of cancer. This article is a general review of BCG in bladder cancer with an emphasis on the indication and mechanism of action in reducing recurrence and progression.