Response Evaluation Criteria In Solid Tumours (RECIST) remain an integral part of the assessment of tumour burden in many clinical trials in oncology; these criteria are used to evaluate the activity and efficacy of new cancer therapeutics in solid tumours. We aim to define the purpose of RECIST, and reflect on the level of documentation needed to enable changes for these criteria to develop a new RECIST. Maintaining the applicability of RECIST as a standard evaluation approach is associated with many challenges, in particular with maintaining a balance between the specificity and generalizability, continued validation and innovation, and use of RECIST in early phase versus late-phase drug development, as well as its relevance in clinical trials versus clinical practice. Key questions relate to different modes of actions of new classes of treatments and new imaging modalities; thus, the RECIST Working Group remains committed to maintain RECIST as a standard for the oncology community.