The Efficient Market Hypothesis (EMH) maintains that financial markets are "informationally efficient". According to EMH, stock prices in an efficient market follow a random walk, meaning they are unpredictable and solely influenced by new information. The hypothesis comes in three forms: weak, semi-strong, and strong. The weak form suggests that all past trading information is incorporated in current prices; the semi-strong form states that all publicly available information is reflected in prices; and the strong form asserts that all information, public and private, is accounted for in asset prices. Critics argue that markets can be inefficient, noting instances of market bubbles and behavioral finance phenomena where investor psychology influences prices.