Purpose: While calls have been made for exercise to become standard practice in oncology, barriers to implementation in real-world settings are not well described. This systematic scoping review aimed to comprehensively describe barriers impeding integration of exercise into routine oncology care within healthcare systems. Methods: A systematic literature search was conducted across six electronic databases (since 2010) to identify barriers to implementing exercise into real-world settings. An ecological framework was used to classify barriers according to their respective level within the healthcare system. Results: A total of 1,376 results were retrieved; 50 articles describing implementation barriers in real-world exercise oncology settings were reviewed. Two hundred and forty-three barriers were identified across all levels of the healthcare system. Nearly 40% of barriers existed at the organizational level (n = 93). Lack of structures to support exercise integration and absence of staff/resources to facilitate its delivery were the most common issues reported. Despite the frequency of barriers at the organizational level, organizational stakeholders were largely absent from the research. Conclusions: Implementing exercise into routine cancer care is hindered by a web of interrelated barriers across all levels of the healthcare system. Organizational barriers are central to most issues. Future work should take an interdisciplinary approach to explore best practices for overcoming implementation barriers, with organizations as a central focus. Implications for Cancer Survivors: This blueprint of implementation barriers highlights critical issues that need to be overcome to ensure people with cancer have access to the therapeutic benefits of exercise during treatment and beyond.