Bladder cancer is the 10th most frequently diagnosed cancer worldwide with 5-year survival rate around 70%. The current first-line treatment for intermediate and high non-muscle invasive bladder cancer (NMIBC) is transurethral resection of bladder tumours followed by intravesical Mycobacterium Bovis Bacillus Calmette-Guerin (BCG) immunotherapy. This a treatment that has not changed significantly since the 1970s. Tumour recurrence rate post-BCG is still high ranging from 31% to 78% within five years. New insights into the immune microenvironment in NMIBC as well as the development of novel viral immunotherapies are set to change the standard of care, and open the door to more effective and better tolerated treatments. Oncolytic viruses have been extensively evaluated in what is a ideal clinical model of cancer gene therapy. Both non-replicating and replicating agents are beginning, finally, to make a significant impact on patient outcomes in the phase 3 clinical trial setting.