Models of daytime and nighttime on-call responsibilities for residents vary across internal medicine training programs, but there are few data regarding residents' perceptions of their on-call experiences. The authors sought to understand what residents perceive as the benefits and detriments of 24-hour, in-house call, a perspective instrumental to informing change. The authors conducted in-depth individual interviews and focus groups between December 2018 and March 2019 with 17 internal medicine residents from postgraduate years 1, 2, and 3 at the University of Toronto about their on-call experiences. Using constructivist grounded theory, the authors developed a framework to understand the residents' perceived benefits and drawbacks of 24-hour in-house call. Residents' experiences on call were grouped into 7 themes regarding negative and positive aspects of call. Participants reported multidimensional fatigue related to call, including decision fatigue, emotional fragility and lability, and loss of empathy, and also reported that call adversely affected their personal lives. Residents expressed conflicting opinions as to whether prolonged duty hours affected patient outcomes. In contrast, residents also expressed benefits to call, including that overnight call led to increased autonomy and decision-making skills and provided preparation for future careers as independent internists. They described developing camaraderie and a sense of belonging to a team with coresidents overnight. Lastly, residents described occupying different roles during regular duty hours and while on call-daytime roles revolved around follow-up of previously admitted patients and administrative tasks, while overnight duties centered on initial workup and medical stabilization of referred patients. Understanding the nuanced phenomenon of being on call from the perspective of those who live through it is a critical step in creating evidence-based educational policies. New call models should emphasize resident autonomy and decision making and should include a consideration of residents' perceived differences between daytime and on-call roles. Copyright © 2020 by the Association of American Medical Colleges.