Factors that place constraints on radio-chemists who are seeking to design and develop radiopharmaceuticals for PET imaging studies include the short half-lives of 11C and 18F, minimum radiochemical yield and specific activity requirements, and high radiation fields that are associated with multi-Curie quantities of PET radionuclides. Nevertheless, during the past 20 years, considerable progress has been made in the development and application of a variety of PET radiotracers for a range of imaging studies in human subjects. We have highlighted a few areas of radiochemistry that focused on PET radiotracers that are described in this issue. Although the number of PET radiotracers synthesized is in the hundreds [6], much work remains to develop specific and useful PET radiotracers for a host of new and exciting noninvasive imaging applications.