This paper studies how hedge fund activism impacts corporate innovation. Firms targeted by activists improve their innovation efficiency over the five-year period following hedge fund intervention. Despite a tightening in research and development (R&D) expenditures, target firms increase innovation output, as measured by both patent counts and citations, with stronger effects among firms with more diversified innovation portfolios. Reallocation of innovative resources, redeployment of human capital, and change to board-level expertise all contribute to improve target firms’ innovation. Additional tests help isolate the effect of intervention from alternative explanations, including mean reversion, sample attrition, voluntary reforms, or activist stock-picking.

In an “activist risk arbitrage,” a shareholder attempts to improve terms of an announced M&A through public campaigns. Activists target deals with low premiums and those susceptible to managerial conflicts of interest, including going‐private deals and deals in which CEOs receive outsized payments. Activist arbitrageurs are associated with a significant decrease in the probability that targets will be sold to the announced bidders, and an increase in the premium paid, both ex post among surviving deals and ex ante among all deals. Activist arbitrage serves as a governance mechanism in M&A and earns higher returns than passive arbitrage.