The labeling of probes with fluorine-18 [(18)F, β(+); 96.7%] continues to play a considerably important role in the development of positron emission tomography (PET) as a modality for both clinical research and clinical diagnoses. This review summarizes the strategies and recent developments in the fluorine-18 labeling of probes for PET imaging. Problems and issues relating to the practical production of fluorine-18 currently in widespread use are also discussed.