Positron emission tomography (PET) is a noninvasive functional imaging technique that allows assessment of key biological processes important in cancer development and progression. It provides information complementary to conventional anatomic imaging, demonstrating utility in a range of cancer settings from diagnosis, biopsy guidance, tumor stratification and prognostication, and staging and surveillance of disease recurrence. Its ability to evaluate vital processes in tumor biology also makes it a potentially valuable and sensitive tool for assessing therapeutic response. The development of novel PET tracers and improvements in technology will only continue to augment the potential of PET and enhance its attractiveness as an instrument to facilitate drug development. This article will discuss the above issues, using the setting of sarcomas as an example.