Radiation pneumonitis (RP) is a dose-limiting toxicity for patients undergoing radiotherapy (RT) and systemic therapy for lung cancer; however, the optimal practice for diagnosis, management and follow-up remains unclear. We sought to establish expert consensus recommendations for RP management. Following literature review on RP, 9 open-ended questions related to knowledge, risk-reduction, diagnosis and treatment were generated for this first round of a consensus-building Delphi process. International leaders in multidisciplinary thoracic oncology were invited to participate (n = 31). Key statements regarding RP diagnosis and management were generated from responses to produce statements for Round 2. Participants will be solicited regarding agreement/disagreement with statements using a 5-point Likert scale. Subsequent rounds will seek consensus in areas that remain unresolved. For Round 1, a 74% response rate (n = 23; 12 radiation oncologists, 5 clinical oncologists, 6 respirologists) was achieved. Eighty-three percent of respondents were not aware of any guidelines for management of RP and 17% used local guidelines or expert review articles. Clinical history, exam and lab criteria (13 respondents) and imaging (15 respondents) were cited as used for diagnosis, and RTOG (9 respondents) and CTCAE grading (14 respondents) for assessment. Radiation-specific factors predictive of RP included irradiated lung volume (especially V20), dose, RT technique and location. The majority of clinical and radiation oncologists used motion management, image guidance and IMRT planning to achieve dosimetric constraints and minimize normal lung dose. Systemic therapy-related RP predictive factors included adjuvant or concurrent chemotherapy, immunotherapy (IO), and use of other pulmonotoxic medications. Patient-related predictive factors included lung function, autoimmune disease, age, performance status and smoking status. Majority of clinicians use risk stratification of patients in order to mitigate RP. Respondents uniformly agreed that steroid therapy is the mainstay of treatment for moderate to severe RP, with variability in the dosing and tapers used. A multidisciplinary management approach was favored by all, including radiation and medical oncologists, respirologists, thoracic radiologists and/or infectious disease or rheumatology specialists if indicated. The majority believe that IO will add complexity in identifying RP. Regarding additional measures to prevent RP in IO patients, respondents were split, with 50% taking additional measures and 50% not, though majority favored monitoring by oncologists during IO cycles and counseling patients on increased RP risk. Responses from international thoracic oncology experts highlight areas lacking consensus in the diagnosis and management of RP. These data will inform the next round of Delphi questions, with an aim of reaching consensus on this common issue.