Accurate assessment of disease response is the foundation of therapeutic trails, which is why the Response Evaluation Criteria in Solid Tumors (RECIST) serve as an international standard that investigators can utilize when examining patient outcomes. Nine years after the initial RECIST criteria were released, an update, RECIST 1.1, was published to improve on the initial criteria and address technologic advancements in imaging. Since then, advancements in both standard clinical and trial practices, combined with improvements in our understanding of cancer biology, have resulted in the identification of a number of limitations of the current RECIST 1.1, either in lack of clear guidance with regard to its best application or in potential benefit of capturing imaging-related data beyond standard categorical response details. As several of these situations reflect the consequences of prolonged control of metastatic disease by using targeted therapies, thoracic oncology has generated many of the key scenarios requiring elucidation and/or improvements. This article specifically examines current controversies in the interpretation and/or optimal utilization of RECIST 1.1, focusing on examples from thoracic oncology, and makes proposals, where possible, on how best to address these issues. These situations include addressing central nervous system versus extra–central nervous system response and progression, depth of response, oligoprogression versus polyprogression, continuation of systemic therapy after use of a local ablative therapy, and the impact of fluctuations in measurements bridging partial response and stable disease categories during prolonged therapy.