This article tries to examine the effi ciency market hypothesis. Therefore, the effi ciency is studied through endogenous and exogenous information. The goal of this paper is to describe the literature review the most exhaustive of effi ciency studies. We show that distinct conclusions can be emphasized following the type of analyzed information. Consequently, the endogenous information is not of quality to question the effi ciency, rather than the exogenous one shows signifi cant results. The exogenous information allows forecasting future stock returns, and earning profi t. It is getting a decision making tool.