Background: There is uncertainty in deferred active treatment (DAT) programmes, regarding patient selection, follow-up and monitoring, reclassification, and which outcome measures should be prioritised. Objective: To develop consensus statements for all domains of DAT. Design, setting, and participants: A protocol-driven, three phase study was undertaken by the European Association of Urology (EAU)-European Association of Nuclear Medicine (EANM)-European Society for Radiotherapy and Oncology (ESTRO)-European Association of Urology Section of Urological Research (ESUR)-International Society of Geriatric Oncology (SIOG) Prostate Cancer Guideline Panel in conjunction with partner organisations, including the following: (1) a systematic review to describe heterogeneity across all domains; (2) a two-round Delphi survey involving a large, international panel of stakeholders, including healthcare practitioners (HCPs) and patients; and (3) a consensus group meeting attended by stakeholder group representatives. Robust methods regarding what constituted the consensus were strictly followed. Results and limitations: A total of 109 HCPs and 16 patients completed both survey rounds. Of 129 statements in the survey, consensus was achieved in 66 (51%); the rest of the statements were discussed and voted on in the consensus meeting by 32 HCPs and three patients, where consensus was achieved in additional 27 statements (43%). Overall, 93 statements (72%) achieved consensus in the project. Some uncertainties remained regarding clinically important thresholds for disease extent on biopsy in low-risk disease, and the role of multiparametric magnetic resonance imaging in determining disease stage and aggressiveness as a criterion for inclusion and exclusion. Conclusions: Consensus statements and the findings are expected to guide and inform routine clinical practice and research, until higher levels of evidence emerge through prospective comparative studies and clinical trials. Patient summary: We undertook a project aimed at standardising the elements of practice in active surveillance programmes for early localised prostate cancer because currently there is great variation and uncertainty regarding how best to conduct them. The project involved large numbers of healthcare practitioners and patients using a survey and face-to-face meeting, in order to achieve agreement (ie, consensus) regarding best practice, which will provide guidance to clinicians and researchers.