In this summary of their recent article in the Review of Financial Studies, the authors provide an overview of the methods and findings of the first comprehensive study of worldwide hedge fund activism—one that examined the effectiveness of some 1,740 separate “engagements” of public companies by 330 different hedge funds operating in 23 countries in Asia, Europe, and North America during the period 2000‐2010.The study reports, first of all, that the incidence of shareholder activism is greatest in companies and countries with high institutional ownership, particularly U.S. institutions. In virtually all countries, with the possible exception of Japan, large holdings by institutional investors increased the probability that companies would be targeted by activists. Nevertheless, in all countries (except for the United States), foreign institutions—especially U.S. funds investing in non‐U.S. companies—have played a more important role than domestic institutional investors in supporting activism.The authors also report that those engagements that succeeded in producing “outcomes” were accompanied by positive and significant abnormal stock returns, not only upon the announcement of the activist's block purchase, but throughout the entire holding period. “Outcomes” were identified as taking one of four forms: (1) increases in dividends or stock buybacks; (2) replacement of board members; (3) corporate restructurings such as sales or spinoffs of businesses; and (4) takeover (or sale) of the entire company. But if such outcomes were associated with high shareholder returns, in the many cases where there were no such outcomes, the eventual, holding‐period returns to shareholders, even after taking account of the initially positive market reaction to news of the engagement, were indistinguishable from zero.The authors found that activists succeeded in achieving at least one of their proposed outcomes in roughly one out of two (53%) of the 1,740 engagements. But this success rate varied considerably across countries, ranging from a high of 61% for North American companies, to 50% for European companies, but only 18% engagements of Asian companies—with Japan, again, a country of high disclosure returns but unfulfilled expectations and disappointing outcomes. Outcomes also tended to be strongly associated with the roughly 25% of the total engagements that involved two or more activists (referred to as “wolfpacks”) and produced very high returns.