Total body PET, or long axial field-of-view PET, is a PET scanner with an extended axial coverage compared with conventional PET scanners. The significant gain in sensitivity of these systems enables shorter scanning times, delayed imaging or lower injected activities, making PET imaging accessible to a broader range of patient groups, including children, pregnant women, and intensive care patients. Non-invasive quantification is made possible by scanning dynamically most of the body in a single bed position, with most organs of interest within the field-of-view. Furthermore, it makes it possible to perform research in areas such as organ-axes and multi-tracer PET. This chapter provides a comprehensive overview of what this system has to offer to the field of oncology, starting from a theoretical point of view, moving on to possible clinical applications and concluding with a discussion of still underexplored areas and future possibilities.