Cytomegalovirus (CMV) infection is a significant concern for transplant recipients due to its potential to cause significant morbidity and mortality. CMV is a member of the herpesvirus family and remains in the body for life after the initial infection, lying dormant in blood-forming cells. It can reactivate, often without symptoms, and spread to various organs, causing damage. CMV infection is very common, with 50–90% of people having been exposed to the virus at some point. After transplantation, the immune system is weakened, increasing the risk of CMV reactivation. This makes CMV the most frequent opportunistic infection in patients who have received hematopoietic cell transplants (HCT) or solid organ transplants (SOT).