Aaron Adalja and Jura Liaukonyte examine the impact of mandatory GMO labeling on consumer preferences in areas where voluntary non-GMO labeling is customary and popular with consumers. A controversy between scientific consensus about GMO safety and consumer awareness of the science has led industry groups to argue that the need for GMO labeling is moot; still several states saw mandatory-GMO-labeling initiatives. Of these, only Vermont passed a mandatory food labeling law. Here, Adalja discusses the effect of mandatory GMO labeling in a market which was already receptive to voluntary non-GMO labeling.