This book examines the shareholder activism of institutional investors, and the effect of this activism on portfolio performance. By focusing on 118 institutional investors headquartered in the United States, the book is unique in addressing the shareholder activism of a large sample. Institutional shareholder activism is defined to include both traditional mechanisms of influence (ie. filing shareholder proposals) and relationship investing. Institutional owners include private and public pension funds, mutual funds, bank trusts, insurance companies, endowments, and foundations. These institutional owners differ substantially, and these differences lead institutions to use their ownership power to pursue different philosophies and actions. Some institutions follow a passive governance policy, whilst others adopt an activist role. This book seeks to answer four questions: 1: Are institutional owners actively involved in the strategic affairs of companies in their portfolios? 2: Which forms of activism do institutional owners employ (either confrontational mechanisms, such as filing shareholder proposals, or relationship building mechanisms)? 3: Which forms of activism employed are most effective? 4: Does the institutional type affect its pursuit of shareholder activism? In answering these questions, the author suggests new important results, that in many cases are contrary to what prior reports of the activities by a small number of institutional owners may intimate.