Although FDG PET and PET/CT have a well established role in the management of most cancer patients, they also have some limitations. For the last 15-20 years a growing number of non-FDG PET tracers have been used in research. Many of these new PET tracers are being investigated for the non-invasive assessment of different biologic functions in cancer cells. This unique information should contribute to making personalized cancer therapy a reality. This paper reviews the non-FDG PET tracers that are most likely to find clinical application, some of them in the near future.