Protesters marched in many U.S. cities this year demanding labels on foods that contain genetically modified organisms (GMOs). Celebrity chefs joined the movement in support of mandatory labels, saying people have a right to know what they are eating. Meanwhile, food manufacturers poured tens of millions of dollars into campaigns to stop states from enacting GMO labeling requirements. To take stock of scientific evidence underlying concerns about GMO crops, a National Research Council committee began examining the crops’ risks and benefits. It noted that weeds are becoming resistant to glyphosate herbicides used on some crops and insects are becoming resistant to the Bacillus thuringiensis toxin produced by others.