Clinical trials in radiation oncology have improved our translational science and patient care. All patients referred to departments of radiation oncology can be invited to participate in a clinical trial with multiple venues. Study endpoints can include intradepartmental endpoints to improve workflow and patient access as well as interdepartmental clinical translational trials that include the National Clinical Trials Network (NCTN) and industry. The quality of the trial is important to trial outcome and influences interpretation of the results of the study and how the results can be applied to patient care moving forward. Clinical trials in radiation oncology to date have accomplished much, however many important questions remain as patient care matures and systemic therapies become more sophisticated and associated with specific biomarkers and cellular expression products. In this chapter we review the history of clinical trials in radiation oncology and review the current status of the structure of quality assurance in clinical trials. We will review unanswered questions and areas to study in each disease area and how to design strategy for trials to address modern unmet needs in our discipline.