We build a novel dataset of timestamped corporate decarbonization commitments—green pledges—for U.S. public firms by classifying news articles with a large language model and human validation. Firms that announce a green pledge tend to be larger and browner than other firms, both within and across industries. Announcements of green pledges significantly and persistently raise stock prices, consistent with a reduction in the carbon premium. Green pledges also predict a sizable decline in future carbon emissions and emission intensities. The effects on stock prices and emissions are strongest for firms in brown industries. Green pledges thus appear credible, convey relevant new information to investors, and provide meaningful financial incentives to decarbonize.