Context: A large proportion of patients with non-muscle-invasive bladder cancer (NMIBC) fall in the gap between bacillus Calmette-Guerin (BCG)-naive and BCG-unresponsive disease. As multiple therapeutic agents move into this gray area, there is a critical need to define the disease state and establish recommendations for optimal trial design. Objective: To develop a consensus on optimal trial design for patients with BCG-exposed NMIBC, defined as high-grade recurrence after BCG treatment that does not meet the criteria for BCG-unresponsive disease. Evidence acquisition: We conducted a literature review using the Cochrane Library, Medline, and Embase and a review of clinical trials in ClinicalTrials.gov as a basis to generate consensus recommendations for clinical trial design in BCG-exposed NMIBC. Evidence synthesis: BCG-exposed NMIBC encompasses BCG resistance (presence of high-grade Ta or carcinoma in situ [CIS] at 3-mo evaluation after induction BCG) and delayed relapse. Randomized controlled trials are required to compare experimental therapies to a control arm receiving additional BCG, although ongoing BCG shortages may impact our ability to follow an optimal trial design. A placebo should be used in combination with BCG if the treatment arm includes BCG plus a study drug. Trials will either need to separate patients with and without CIS into two cohorts, or stratify by the presence of CIS at the time of randomization. If two cohorts are used, the primary endpoint for CIS patients should be complete response within a predetermined time. The primary endpoint in a cohort with Ta/T1 only, or if a single combined cohort is used, should be the duration of event-free survival. Suggested efficacy thresholds and corresponding sample sizes are provided. Conclusions: The International Bladder Cancer Group has developed recommendations regarding definitions, endpoints, and clinical trial design for BCG-exposed NMIBC to encourage uniformity among studies in this disease state. Patient summary: Our consensus provides a precise definition of the disease state for bladder cancer not invading the bladder muscle and exposed to bacillus Calmette-Guerin (BCG) treatment. Clear guidance for conducting optimal clinical trials in this disease setting was established and we believe that this will promote further progress in this field. (C) 2021 European Association of Urology. Published by Elsevier B.V. All rights reserved.