The Practice Guidelines Committee and the Transplant Infectious Disease Special Interest Group of the American Society for Transplantation and Cellular Therapy developed guidelines focusing on human herpesvirus 6B (HHV-6B). A compendium-style approach was used to address a series of standalone frequently asked questions (FAQs), supported by tables and figures to spotlight key concepts. Adult and pediatric infectious disease and hematopoietic cell transplantation (HCT) content experts developed these FAQs and finalized recommendations after consensus was reached. This ninth topic in the series focuses on the relevant risk factors, diagnostic considerations, prophylaxis, and treatment approaches relevant to HHV-6B infections after HCT and chimeric antigen receptor-T-cell therapy.