Following 2 decades of discussion, the border adjustment tax (BAT) briefly emerged as part of proposed US corporate tax reform in early 2017. While heavily debated, little empirical evidence exists regarding the BAT. We take advantage of the period during which the BAT was under strong consideration to examine its effects on shareholder value. We find that high-importing firms (measured using industry, aggregate government industry data, and firm-level shipping-container data) suffer negative returns on days the tax had a greater likelihood of adoption. We also find that firms lobbying for the BAT experience positive returns over that same time period.