Introduction Objectives: Patients with muscle invasive bladder cancers (MIBC)are managed by a variety of specialists including urologists, medical and clinical or radiation oncologists, pathologists, radiologists and specialist nurses. There are uncertainties around many aspects of disease management where high quality evidence is not available. Bodies like the EAU and ESMO therefore have limited options on which to base clinical practice guideline (CPG)recommendations. So the aim of this project was for the EAU and ESMO to collaborate and survey expert opinion, attempting to seek consensus and provide interim guidance on MIBC management where there is no evidence, low quality evidence, or conflicting evidence. Materials & Methods: Our project steering group, assembled subject specific subgroups. Each subgroup, with an EAU and ESMO co-chair, highlighted areas of uncertainty in their specialist area: strategies for variant histologies; the role of prognostic markers; the role of radiotherapy in the non-metastatic setting; the role of surgery and radiotherapy with curative intent in the metastatic setting; the role of checkpoint inhibitors; and survivorship strategies. They constructed 115 discrete statements in total which were entered in a 2-round Delphi survey. Participants were sampled from international experts identified through professional societies. The participants scored each statement on a scale of 1 (strongly disagree)to 9 (strongly agree)or‘unable to score’. Scoring thresholds were: ≥70% scoring 1-9 and ≤15% scoring 1-3 or vice versa = consensus, all others were considered equivocal. Analyses were stratified by the stakeholder groups which had an informed opinion. Statements not reaching a-priori scoring thresholds were further discussed in a 1-day face-to-face consensus meeting. The meeting consisted of topic-specific breakout sessions where statements which were close to but not reaching consensus from the Delphi were prioritised for discussion. The subgroup chairs then reported back to the plenary sessions where structured discussion and final voting occurred. Results: The project overview and results are described in figure 1. Across two Delphi rounds, 97 experts scored 116 statements, reaching consensus on 42% of the statements. Following the break out sessions and plenary discussion 27 statements with ‘near consensus’ results from the Delphi were discussed by 34 international experts: consensus was reached on 87% of the statements. [Figure Presented]Conclusions: There is some consensus among clinical experts on various aspects of the management of MIBC which may be used to inform practice. However, this is low quality evidence and only interim guidance until better evidence emerges.