Positron emission tomography (PET) has earned an important role in clinical imaging, where it is used almost exclusively as hybrid modality such as PET/CT and PET/MR. The driving force behind the development of the method and the increasing clinical penetration of PET in the past two decades was clearly its use in Oncology. The most used tracer in PET is the 18 F-labeled ﬂ uoro-deoxy-glucose (FDG). With the help of this molecule malignant tumors and their metastases, in which anaerobic glycolysis is typically increased, can be identiﬁ ed with high sensitivity in the total body volume. However, FDG is not a tumor speciﬁ c tracer, thus both false positivity and false negativity may occure which reduces the diagnostic accuracy. Indications of FDG PET studies in Oncology continuously evolved, owing to scientiﬁ c publications, large scale national programs and even health-economic considerations. This publication describes the well-established indications of FDG PET/CT(MR) tests in cancer diagnostics and furthermore discusses more recent new PET tracers already being applied as well as those expected to be used in the future.