Abstract: This chapter reviews the benefits and costs of using indices, in particular the G- and E-indices, in empirical corporate governance research. As with corporate governance itself, the widespread use of corporate governance indices have both costs and benefits. The literature has identified a number of concerns with the use of these indices including concerns over measurement error, endogeneity, reverse causation, omitted variables and proper identification of the actual mechanisms by which corporate governance might matter. On the other hand, these indices enjoy several important benefits that explain their continued and widespread use. It concludes that event study methodology and the utilization of legal shocks/regulatory discontinuities for identification will likely play an ever greater role in future research.