Learning Objectives: 1) Understand the need for monitoring patient radiation exposures based on the results of national surveys. 2) Learn about the concept of Reference Values (RV's) and their impact on diagnostic radiology. 3) Describe the application of RV's in North America and as adopted by the ACR. 4) Understand the application of Reference Values in Europe and changes which have been observed since implementation. Disclosure: (J.E.G. is Director of Technology at Landauer, Inc)