This lecture provide an overview of how nuclear medicine imaging using positron emission tomography (PET) can be used to provide biochemistry and biophysics information in vivo, from animal model through to the human.An introduction on the basics of PET imaging, including presentations on how a PET scanner works, how radiopharmaceuticals are developed and how physiological information can be extracted from a series of tempo-spacial dynamic PET images.In addition, highlights on the latest PET imaging technology for small and large animal, the use of PET radiotracers for new drug development, and importance of clinical studies using Pet for therapeutic evaluations.