In the past three decades, international and regional human rights bodies have developed an ever-lengthening list of measures that states are required to adopt in order to prevent torture. But do any of these mechanisms actually work? This study is the first systematic analysis of the effectiveness of torture prevention. Primary research was conducted in 16 countries, looking at their experience of torture and prevention mechanisms over a 30-year period, and data were analysed using a combination of quantitative and qualitative techniques. The results show that prevention measures work, but some are much more effective than others. Most important of all are the safeguards that should be applied in the first hours and days after a person is taken into custody. Notofication of family and access to an independent lawyer and doctor have a significant impact in reducing torture. The investigation and prosecution of torturers and the creation of independent monitoring bodies are also vital. An important caveat to the conclusion that prevention works is that it is the actual practice in police stations and detention centers that matters - not treaties ratified or laws on the statute book.