Contrarian investing involves buying beaten-down stocks or the entire market when they are down, with the expectation that they will recover. There are different forms of contrarian investing, including knee-jerk, technical, constrained, and opportunistic contrarianism. Knee-jerk contrarianism involves buying any traded asset that has fallen significantly in price, based on the belief that what goes down will always come back up. The evidence for this strategy comes from historical data on equity markets, which show that stocks deliver the highest returns over long periods. However, there are caveats to this approach, including selection bias and the risk of buying into a market downturn. Technical contrarianism involves buying stocks or markets when they are down, but only if charting or technical indicators support the decision. Research has shown that technical indicators can provide signals of shifts in market mood and momentum. Constrained contrarianism involves buying beaten-up stocks, but only if they meet certain criteria, such as high profitability, strong moats, and low risk. This approach aims to avoid value traps, where a company looks cheap but proceeds to become even cheaper. The evidence suggests that adding quality screens to value screens can improve returns, but the payoff is not always significant.