A great deal of knowledge about metabolism has been garnered from mice, but, mice are not people! However, metabolic tissues are often difficult to assess in human subjects. To better understand metabolic physiology, novel approaches and ingenuity have been applied using non-invasive imaging approaches. Recent advances in non-invasive imaging such as MRI and PET have made it possible to describe glucose and fat metabolism in tissues at a level of detail not previously possible. These discoveries have advanced our understanding of human physiology and clinical knowledge. This session will highlight the hottest methods to assess tissue metabolism in vivo and new applications of classic approaches.