PET is an exquisitely sensitive molecular imaging technique using positron-emitting radioisotopes coupled to specific ligands. Many biological targets of great interest can be imaged with these radiolabelled ligands. This review describes the current status of non-18-fluorodeoxyglucose PET tracers that have a potential clinical effect in oncology. With the help of these tracers, knowledge is being acquired on the molecular characterisation of specific tumours, their biological signature, and postinterventional response. The potential role of these imaging probes for tumour detection and monitoring is progressively being recognised by clinical oncologists, biologists, and pharmacologists.