BCG has been used in the treatment of NMIBC for more than 40 years. Nevertheless, its exact working mechanisms have not been completely discovered. Clinical and basic research done over all these years has generated much information but it could be summarized in a few simple statements. It has been demonstrated the best route of administration is intravesical, BCG is superior than intracavitary chemotherapy to prevent recurrence but its adverse events are worse. Recently, it has been demonstrated that BCG could delay or prevent progression to infiltrative cancer. Nevertheless, to achieve this, maintenance therapy is necessary. Therefore, the recommendation is to treat middle and high risk cases with BCG. No significant differences in efficacy have been found between the various strains but differences in recurrence have been found between standard and reduced doses.Furthermore, the presence or absence of side effects does not seem to be a prognostic factor for the efficacy of BCG and, maintenance therapy is not associated with a significant increase in toxicity. In the future, the optimal schedule and doses must be defined, and it probably will be different for each individual. BCG shortage has led to try alternative therapies through chemo hyperthermia or electrical gradient application the efficacy of which should be evaluated. New strains and immunological treatments are also under research.