Positron emission tomography (PET), the imaging of pharmaceuticals labeled with positron-emitting radionuclides, is a rapidly growing modality for the diagnosis and management of cancer. PET yields high-quality images characterizing substrate metabolism, cellular proliferation, receptor density, and other parameters that can be used to identify cancer and evaluate its response to therapies. The technique mainly utilized in cancer management is FDG-PET, which exploits the abnormal glucose metabolism of cancer cells first characterized by Warburg. We discuss the principles of PET, the currently available instrumentation and radiopharmaceuticals, the efficacy of FDG-PET in the management of cancer, and the prospects for near-term advances in cancer using PET.