Unfortunately, there is no universally accepted definition of the Equity Risk Premium. Available material on the theme are very broad and deep, ranging from ex-post analysis on historical data -with distinct samples in different time periods- to ex-ante estimates of the equity premium making use of several models based in variables such as risk aversion, consumption growth, accounting data and dividend yield, among others. The objective of this paper will be to analyze a compilation of several approaches taken, their results and contributions. In face of the significant differences presented when computing the equity premium, it is key for the investor who will make use of the equity premium estimate to know clearly which definition of the premium he will be using and why is that definition appropriate for his particular purpose. In the final chapter we will estimate the equity risk premium in Brazil based on a study developed in 1993 by McKinsey and Company, Inc.