Stop-loss rules are trading rules that involve selling a security when its price drops by a certain amount and buying the security back when its price rises above a pre-specified level. They are popularly used by practitioners. These rules are designed to protect gained profits as their sale trigger the price to be adjusted higher as prices increase. This thesis contributes to the literature on stop-loss rules in financial markets. The first essay investigates the time-series and cross-sectional determinants of stop-loss rules for risk reduction in the U.S. stock market. It finds that, even though stop-loss rules have poorer mean returns to a mean-variance optimal benchmark, they are effective at stopping losses. These rules reduce over...