Cytomegalovirus (CMV) infection and disease are important causes of morbidity and mortality in transplant recipients. For the purpose of developing consistent reporting of CMV outcomes in clinical trials, definitions of CMV infection and disease were developed and most recently published in 2002. Since then, there have been major developments in its diagnosis and management. Therefore, the CMV Drug Development Forum consisting of scientists, clinicians, regulators, and industry representatives has produced an updated version incorporating recent knowledge with the aim to support clinical research and drug development. The main changes compared to previous definitions are the introduction of a “probable disease” category and to incorporate quantitative nucleic acid testing in some end-organ disease categories. As the field evolves, the need for updates of these definitions is clear, and collaborative efforts between scientists, regulators, and industry can provide a platform for this work.