Abstract: As a result of movements for labeling food with genetically modified organisms (GMOs) Congress enacted a mandatory labeling requirement in 2016. These movements, and the legislation, raise recurring questions about mandatory product labels: whether there is a market failure, neoclassical or behavioral, that justifies them, and whether the benefits of such labels justify the costs. The first goal of this essay is to identify and to evaluate the four competing approaches that agencies now use to assess the costs and benefits of mandatory labeling in general. The second goal is to apply those approaches to the context of GM food. Assessment of the benefits of mandatory labels presents especially serious challenges. Agencies have (1) claimed that quantification is essentially impossible; (2) engaged in breakeven analysis; (3) projected various endpoints, such as health benefits or purely economic savings; and (4) relied on private willingness to pay for the relevant information. All of these approaches run into serious normative and empirical challenges. In principle, (4) is best, but in practice, (2) is sometimes both the most that can be expected and the least that can be demanded. Many people favor labeling GM food on the ground that it poses serious risks to human health and the environment, but with certain qualifications, the prevailing scientific judgment is that it does no such thing. In the face of that judgment, some people respond that even in the absence of evidence of harm, people have “a right to know” about the contents of what they are eating. But there is a serious problem with this response: there is a good argument that the benefits of such labels would be lower than the costs. Consumers would obtain no health benefits from which labels. To the extent that they would be willing to pay for them, the reason (for many though not all) is likely to be erroneous beliefs, which are not a sufficient justification for mandatory labels. Moreover, GMO labels might well lead people to think that the relevant foods are harmful and thus affirmatively mislead them. Some people contend that GMOs pose risks to the environment (including biodiversity), to intelligible moral commitments, or to nonquantifiable values. Many people think that the key issue involves the need to take precautions in the face of scientific uncertainty: Because there is a non-zero risk that GM food will cause irreversible and catastrophic harm, it is appropriate to be precautionary, through labels or through more severe restrictions. The force of this response depends on the science: If there is a small or uncertain risk of serious harm, precautions may indeed be justified. If the risk is essentially zero, as many scientists have concluded, then precautions are difficult to justify. The discussion, though focused on GM foods, has implications for disclosure policies in general, which often raise difficult questions about hard-to-quantify benefits, the proper use of cost-benefit balancing, and the appropriate role of precautionary thinking.