Abstract
Hedge fund activism emerged as a major force of corporate governance in the 2000s. By the mid-2000s, there were between 150 and 200 activist hedge funds in action each year, advocating for changes in 200–300 publicly listed companies in the United States. In this article, we review the evolution and major characteristics of hedge fund activism, as well as the short- and long-term impacts of the performance and governance of targeted companies. Though most of the analyses here are based on a comprehensive sample of over 2,000 activism events in the United States from 1994 to 2011, hand-collected by the authors from regulatory filings and news searches, this article covers all major studies on the topic, including those on markets outside of the United States.