Intravesical immunotherapy with bacillus Calmette-Guérin (BCG) is the standard of care for high-risk and intermediate-risk non-muscle-invasive bladder cancer (NMIBC). Several BCG strains are available. Despite originating all from subcultures of the same Mycobacterium, strains are genetically different which may lead to differences in treatment efficacy and adverse events. Identification of a more efficient strain and assessing its optimal administration schedule may improve oncological outcomes in NMIBC, specifically because of the worldwide shortage in BCG availability. This review focused on the antitumor effect of different BCG strains with a particular emphasis on the evidence underlying BCG dose and treatment schedules.