This supplement, Immuno-Oncology Therapy Essentials: Proactive Management of Immune-Related Adverse Events, highlights the IO Essentials tools for prompt recognition and management of the irAEs associated with checkpoint inhibitor therapy across tumor types—from melanoma, to other solid tumors, to hematologic malignancies. Featuring articles on telephone triage and acute care recommendations; non–small cell lung cancer;  head and neck squamous cell carcinoma; and a pan-tumor review.