The 113th Congress extended the research and development (R&D) tax credit through the end of 2014 by passing the Tax Increase Prevention Act (H.R. 5771), which President Obama signed into law on December 19, 2014. That the fate of this credit in 2015 remains unknown is not surprising. This brief explores the history, logistics, and policy implications of the temporary R&D tax credit, and offers recommendations for additional research that would help determine the merit of making the credit permanent. Using new, restricted-access IRS data and an instrumental variables strategy, the brief offers an unbiased estimation of the effectiveness of the R&D tax credit, showing that corporate research intensity—the ratio of R&D spending to sales—is indeed highly sensitive to the tax subsidy rate. When it gets cheaper for firms to spend on qualified R&D, they actually do spend more, as policymakers hope.