Since they were first commercially grown in the mid-1990s, genetically engineered (GE) crops have expanded across the globe, offering farmers the advantages of genetically enhanced resistance to drought, herbicides, and insects. According to the International Service for the Acquisition of Agri-Biotech Applications (ISAAA), a crop biotechnology advocacy organization, farmers in 29 countries grew nearly 400 million acres of commercial GE crops in 2011, an 8% increase from the previous year.1 An estimated 60–70% of processed foods in the United States contain GE ingredients,2 and GE corn and soybeans make up the majority of the U.S. crop.3 But while GE crop acreage has been steadily increasing, so have concerns in some quarters that producing and eating GE foods may pose unexpected environmental and health hazards. In the absence of strong health and safety data, many national governments across the world have taken steps to minimize the presence of GE food within their borders. In Europe, six nations (Austria, France, Germany, Greece, Hungary, and Luxembourg) have enacted bans on the cultivation and import of GE products,4 and nearly 50 nations worldwide require that all GE foods be labeled as such.5 In the United States, consumer concern about GE foods has been slower to surface. But that’s changing—and a ballot question this fall in California has the potential to radically alter the GE landscape throughout the rest of the United States. On 6 November 2012 California voters will decide whether foods containing genetically modified organisms (GMOs) must be labeled. If passed, the California Right to Know Genetically Engineered Food Act—also known as Proposition 37—would require that all raw food products containing GMOs be labeled as “genetically engineered” and that any processed foods containing GMOs be labeled as “partially produced with genetic engineering” or “may be partially produced with genetic engineering,” with implementation due 1 July 2014.6 The law would exempt meat, dairy, and other products from animals that consumed feed containing GMOs but would cover such products from animals that were themselves genetically engineered. It would also exempt food sold in restaurants and alcohol. The initiative has touched off a heated battle in the Golden State. On one side, pro-labeling advocates claim the safety of GE foods is unknown and that consumers have the right to know what’s in their food. Opposing them are an array of groups in mainstream agribusiness, the grocery industry, and the biotech industry, many of whom would bear the cost of implementing new labeling as well as potential loss of sales to wary consumers who aren’t sure what the labels mean or whether they should be worried. Kathy Fairbanks, spokeswoman for the Coalition Against the Deceptive Food Labeling Scheme, which represents these groups, claims the initiative would “force California families to pay hundreds of dollars more in higher food prices, would cost millions in government bureaucracy, and would not provide any health and safety benefits.” The coalition also says the bill’s many exemptions make no sense and will only confuse and mislead consumers, asking on its website, “If Prop 37 was really about the ‘right to know,’ why did proponents include so many special-interest exemptions?”7 But Stacy Malkan, Fairbanks’ counterpart for the pro-labeling organization California Right to Know, says there’s no evidence to support the claim that Californians’ grocery bills would go up if the labeling measure passes. She also says that while there’s no conclusive evidence that GE foods are unsafe, there also is no conclusive evidence that they are. “Many scientists are saying that in the face of scientific uncertainty, labeling is an important tool to help track potential health risks,” she says. Michael Hansen, a senior staff scientist at Consumers Union, offers a theoretical example of how such tracking might work: “If you take a gene from the kiwi fruit, put it into a tomato, and the tomato gets turned into sauce for your pizza, and there’s an allergic reaction, only the genetically altered tomato would produce that allergic reaction. . . . This is not like [allergy concerns associated with] conventional foods because the problem is going to be for one particular [bioengineered modification]. How are you going to figure that out unless it’s labeled? You can’t. And that’s why so many countries have labeling.”