In this issue of PET Clinics, guest editor Dr. Rathan M. Subramaniam brings his considerable expertise to the topic of Clinical PET/CT: Quarter-Century Transformation of Oncology. The first PET-CT prototype for clinical evaluation was installed at the University of Pittsburgh Medical Center in 1998, and combined PET/CT scanners perform almost all PET scans today. These combined scans help pinpoint abnormal metabolic activity and may provide more accurate diagnoses than the two scans performed separately. In this issue, top experts discuss specific cancers where PET/CT is used and how it has transformed diagnosis in that area.