The Efficient-Market Hypothesis (EMH) is a central concept in financial economics, stating that asset prices fully reflect all available information, making it impossible to consistently "beat the market" on a risk-adjusted basis. This foundational idea is closely associated with Eugene Fama, partly due to his influential 1970 review, and builds on earlier work by figures like Bachelier and Mandelbrot. The EMH suggests that any new information is rapidly incorporated into prices as investors act on it, thus eliminating opportunities for easy, risk-free profits. Early empirical studies, such as those by Alfred Cowles in the 1930s and 1940s, often found that professional investors struggled to outperform the market and that stock prices largely followed a random walk in the short term, leading to ongoing debate about market anomalies and the extent of long-term predictability.