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This paper examines the efficiency market hypothesis through endogenous and exogenous information. The aim of this article is to make an exhaustive literature review of efficiency studies. This paper shows that distinct conclusions can be highlighted following the type of analyzed information. Hence, the endogenous information is not of a quality to question the efficiency, but rather the exogenous one shows significant results. The exogenous information allows forecasting future returns, and earning profit. It is a real decision-making tool.JEL Codes: G00, G14