Infectious diseases are important causes of morbidity and mortality in patients with cancer. The NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines) for Prevention and Treatment of Cancer-Related Infections characterize the major pathogens to which patients with cancer are susceptible, with a focus on the prevention, diagnosis, and treatment of major common and opportunistic infections. This portion of the guidelines highlights the sections on antifungal and antiviral prophylaxis. Antifungal and antiviral prophylaxis recommendations have expanded over the past few years. New agents for the treatment of fungal infections and incorporation of therapeutic drug monitoring are presented. Antiviral prophylaxis for hepatitis B and management considerations for hepatitis C and HIV have been further developed.