This book studies the impact of investor biases on investment decisions of Pakistani stock investors. Investors take many decisions in stock market on daily basis but could not avoid investor biases which they are facing during this decision-making process. For this, researcher carried this study to analyze investors biases in detail, its impact on investment decisions and the influence it has on individual investor at Pakistan Stock Exchange. The research had two primary aims; first to analyze the impact of investor biases on investment decisions of Pakistan stock investors, and second to find which of investor biases have high, moderate, low, positive or negative, statistically significant and insignificant impact on investment decision making. The study will use Kahneman & Tversky (1979) Prospect theory as the main theoretical framework, for analyzing impact of four investor biases such as: Overconfidence bias, conservatism bias, herding effect bias and availability bias on investment decisions of investors.