Buying or selling a financial asset following the community in financial markets is a common behavior. Herd behavior is the decision of the individual influenced by the majority, rather than own opinions, by being affected by the behavior of other individuals. Herd behavior may occur due to reasons such as the individual's lack of efficient information or confidence in own knowledge, as well as psychological factors distracting the individual from rationality, like following the trend. Professional managers and individual investors can follow the herd behavior. In markets dominated by uncertainty and in economic conditions where volatility is observed, investors try to avoid risks by following the generally accepted view in the market, unlike rationality assumption. Herd behavior causes the efficiency of markets to deteriorate and affects asset pricing process. Herd behavior has been suggested as an important behavioral factor especially in times of in financial crisis.