The efficient market hypothesis (EMH) is a theory in financial economics that states that asset prices reflect all available information. This means that it is impossible to consistently achieve returns that outperform the market because stock prices already reflect all known information. EMH is based on the idea that in an efficient market, at any given time, prices fully reflect all available information, and as a result, it is impossible to consistently achieve returns that outperform the market. There are three forms of the efficient market hypothesis: the weak form, the semi-strong form, and the strong form. The weak form asserts that all past prices of a stock are reflected in today's stock price, making it impossible to profit from historical price information. The semi-strong form states that all publicly available information is reflected in stock prices, making it impossible to achieve excess returns using publicly available information. The strong form goes further to claim that all information, both public and private, is reflected in stock prices, making it impossible to achieve excess returns even with insider information. EMH has significant implications for investment strategies. If the market is truly efficient, it suggests that actively managed funds may not consistently outperform passive index funds over the long term. However, critics of the efficient market hypothesis argue that there are inefficiencies in the market that can be exploited through various investment strategies, such as value investing or technical analysis. Overall, the efficient market hypothesis continues to be a topic of debate and research in the field of finance.