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This paper exploits a differential increase in copyright under the UK Copyright Act of 1814 - in favor of books by dead authors – to examine the influence of longer copyrights on price. Difference-in-differences analyses, which compare changes in the price of books by dead and living authors, indicate a substantial increase in price in response to an extension in copyright length. By comparison, placebo regressions for books by dead authors that did not benefit from the extension indicate no differential increase. Historical evidence suggests that longer copyrights increase price by improving publishers' ability to practice intertemporal price discrimination.