Background: Immune checkpoint inhibitors (ICIs) have revolutionized treatment for melanoma and lung cancer and are in widespread use. This study aims to describe how patients and caregivers learn about ICI toxicities and their lived experiences of receiving an ICI. Methods: We conducted a qualitative study of patients with advanced cancer receiving ICIs from a single academic center and their caregivers. We purposively sampled patients with stage IV non-small cell lung cancer (n=16) or stage III (n=9) or IV (n=17) melanoma who were initiating or discontinuing an ICI. We conducted semi-structured interviews to explore patients' and caregivers' experiences learning about and living with ICI toxicity. We used a framework approach to analyze interview transcripts, which included developing a codebook, double-coding transcripts, and synthesizing codes into themes with a multidisciplinary research team. Results: The median age of patients was 68 years, 31% were female and 49% had at least a college degree. We identified the following themes: i) Patients initiating ICIs received exhaustive counseling about side effects (“everything from rash to death,”“like a drug ad on television”), yet some patients lost details in the deluge of information (“I'm sure I was told of the risk, I just can't specifically recall what”); ii) Patients and caregivers identified several factors that helped them feel comfortable to proceed with treatment, namely that the oncology team emphasized the infrequency of serious side effects and that the team was ready to manage whatever toxicity occurred. In addition, patients perceived that ICI benefits outweighed the risks or felt that they had no alternative; iii) Among patients who discontinued ICIs, the association between ICI toxicity and efficacy was a source of hope (“I hope every day to find vitiligo... that might say that the immunotherapy is working”); iv) Patients’ and caregivers’ impressions of ICIs depended on patients’ outcomes. Patients tolerating ICIs well and their caregivers were surprised at how easy their treatment was, whereas patients who discontinued ICIs after experiencing severe side effects felt frustrated and surprised by toxicity, or worried their cancer would progress. Conclusions: Patients receiving ICIs for advanced cancer and their caregivers felt they received comprehensive education about ICI toxicity. They appreciated when their oncology team provided reassurance that side effects were rare and manageable, as well as messages that framed toxicity as a sign of efficacy once they occurred. Even with excellent preparation for the possibility of toxicity, patients who experienced severe toxicity were still surprised and disappointed. These perspectives highlight patient and caregiver preferences for learning about ICIs and opportunities to support patients in coping with advanced cancer.