Investors have long been unhappy with certain governance arrangements adopted by companies undertaking initial public offerings ("IPOs"), such as dual-class voting structures. Traditional sources of corporate governance rules-the Securities and Exchange Commission, state law, and exchange listing rules-do not constrain these arrangements. As a result, investors have turned to a new source of governance rules: index providers. This Article provides a comprehensive analysis of index exclusion rules and their likely effects on insiders ' decision-making. We show that efforts to portray index providers as the new sheriffs of the U.S. capital markets are overstated. Index providers face complex and conflicting interests, which make them reluctant regulators, at best. We put forward an analysis of insider incentives in light of index exclusions and apply it to one of the most important applications ofindex exclusion rules to date, the recent decision by index providers to exclude from their indexes certain companies with dual-class share structures. We conclude that the efficacy of index exclusions in preventing disfavored arrangements such as dual-class structures is likely to be limited, but not zero. Index exclusions are a corporate governance experiment, one that has important lessons. We examine these lessons, and the way forwardfor corporate governance. These lessons are all the more important because of the central place of index funds, and therefore index providers, in our capital markets.