How do barriers to the diffusion of academic research affect innovation? In 2008, the National Institutes of Health (NIH) mandated free online availability of funded research. This policy caused a 50 percentage point increase in free access to funded articles. We introduce a novel measure, in-text patent citations, to study how this mandate affected industry use of academic science. After 2008, patents cite NIH-funded research 12% to 27% more often. Nonfunded research, funded research in journals unaffected by the mandate, and academic citations see no change. These estimates are consistent with a model of search for useful knowledge. Inefficiency caused by academic publishing may be substantial.