This paper surveys the major changes in patent policy and practice that have occurred in the last two decades in the U.S., and reviews the existing analyses by economists that attempt to measure the impacts these changes have had on the processes of technological change. It also reviews the broader theoretical and empirical literature that bears on the expected effects of changes in patent policy. Despite the significance of the policy changes and the wide availability of detailed data relating

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... to patenting, robust conclusions regarding the empirical consequences for technological innovation of changes in patent policy are few. Possible reasons for these limited results are discussed, and possible avenues for future research are suggested.