This chapter reviews empirical data shedding light on whether clinicians can predict that patients will die by suicide, or whether fatalities can be prevented. Based on existing research, there is good evidence that treatment programs, using psychotherapy and medication, can reduce suicide attempts. Yet while patients with suicidal ideations or attempts can be treated successfully, they are not necessarily at high risk for death by suicide. Research on suicide prevention has not shown that fatalities among patients in treatment can be predicted or that clinical interventions can reduce the risk for fatality. Most people who die by suicide are distinct from attempters, while those at highest risk may not necessarily present for treatment. There is also little evidence that hospitalizing suicidal patients prevents fatal outcomes. The strongest evidence for suicide prevention derives from population-based strategies, particularly reducing access to means.