An article from SAGE Crossroads examines a fundamental problem in aging studies: how do you tell if anti-aging therapies are working? For human trials, unlike work on flies, mice or worms, researchers obviously can't just wait and see how each treatment does. Scientists must be able to accurately and quickly measure physical aging in order to determine whether a particular therapy is working. At present, the field of aging biomarkers is somewhat up in the air, with definitive answers remaining elusive. As the article notes, "what now?"