In patients who undergo hematopoietic stem cell transplantation (HSCT), cytomegalovirus (CMV) infection directly or indirectly increases all-cause and non-relapse mortality rates. Although preemptive therapy suppresses CMV infection, it does not improve non-relapse mortality rates in patients with CMV reactivation compared to patients with no CMV reactivation. According to the World Health Organization International Standards (WHO IS), quantitative polymerase chain reaction has been recently adopted as the global standard for monitoring CMV, and maribavir, brincidofovir, and letermovir have been developed as new antiviral drugs for the treatment of CMV infection. Letermovir, a first-class anti-CMV agent, strongly inhibits the CMV DNA terminase complex, which is required for viral DNA cleavage and packaging. It significantly suppressed CMV infection in a phase III clinical trial, thereby improving the overall survival of patients who undergo HSCT. Vaccines and cell therapies for CMV must be further developed.