While the articles in this issue largely illustrate the impact of technical advances, we should emphasize the enormous power that PET gets from biologically relevant probes. This fundamentally provides potential and opportunities yet to be realized. Research into new probes or radiotracers, analysis methods for dynamic imaging, and the development of these into useful tools for clinical medicine and biomedical research are of great importance and represent areas of promise. Similarly, biological and medical investigation conducted with PET as a tool is a very active and important area of research. While there is, and should be, great interest in the development of PET/MRI technology, the impact of these systems in clinical medicine remains a work-in-progress. Research is needed to demonstrate the benefits of these and other advances. In addition, and appropriately, there is strong interest in the development and testing of new applications of PET. Specifically there is great need for improved assessment of many neurological and mental health conditions, and also biomarkers for the development of improved therapies for cancer and cardiovascular disease.