Local governments spend over $12 billion annually funding the operation of 15,427 public libraries in the United States, yet we know little about their effects. We use data describing the near universe of public libraries to show that public library capital investment increases library visits, children’s attendance at library events, and children’s circulation by an average of 5–15 percent in the years following investment. Increases in library use translate into improved test scores in nearby school districts: a $200 or greater per student capital investment in local public libraries increases reading test scores by 0. 01–0.04 standard deviations in subsequent years. (JEL G31, H75, I21, L86)