Epidemiological considerations point to a small handful of prevention strategies that have the potential for dramatically reducing suicide rates. Nearly all of those prevention approaches involve population-based strategies to either find an increased number of individuals at high risk for suicide or to reduce the prevalence of risk factors in members of a population that, as a whole, has a relatively low rate of suicide. Few of these approaches have been evaluated in rigorous trials. We argue that there are rigorous randomized trial designs that are both feasible and ethical and can be used to test both programmes and implementation strategies for population-based suicide prevention. We review existing suicide prevention trials and introduce two new randomized trial designs that are likely to achieve sufficient statistical power. The 'dynamic wait-listed design' randomizes across different time periods and is now being used to test a gatekeeper training programme in 32 schools. It could also be used to examine suicide prevention programmes in rural areas. The multi-trial follow-up study builds on the large number of successful population-based preventive interventions aimed at reducing known risk factors for suicide in youths to see whether these also cause a reduction in rates of completed suicide.