Suicide is the act of intentionally inflicting one's own death. While suicide deaths are uncommon, suicide attempts and ideation (thought of killing oneself or wishing oneself dead) are less rare. Suicidal ideation is much more common than suicide attempts and is often a precursor of suicide and can be targeted by intervention. Self-harm is the broader term that encompasses suicide attempts and self-injurious behavior without the conscious or certain intent to cause one's own death. It can be difficult, however, to determine the intent of the patients who injure themselves. Among adults, for example, almost half with a lifetime history of a suicide attempt report that their attempt was a cry for help and they did not want to die. While the current review is focused on suicide, suicide attempts, and suicidal ideation, studies examining self-harm rather than suicide attempts may be included in this review if the majority of cases are either suicide-related or are cases with unknown intent. While we use the term "suicide attempt" preferentially over "self-harm" when discussing primary research, we do use the terms the authors use in their description of the study. This review provides updated evidence regarding the accuracy and reliability of instruments used to screen for increased suicide risk, benefits and harms of screening for increased suicide risk, and benefits and harms of treatment to prevent suicide. The USPSTF will use this review to update its 2004 recommendation for primary care practices. This review includes all trials from the previous review that met current inclusion/exclusion criteria, as well as newly identified studies. We developed an analytic framework and Key Questions (KQs) using USPSTF methods to guide our literature search, in consultation with liaisons from the USPSTF. The KQs we examined were: 1. Do screening programs to detect suicide risk among adolescents, adults, and older adults in primary care settings result in improved health outcomes (decreased suicide attempts, decreased suicide deaths, improved functioning, improved quality of life, or improved health status) or intermediate outcomes (decreased suicidal ideation, depressive symptomatology, or hopelessness)? Does the effect of screening programs vary by population characteristics (i.e., sex, age, race/ethnicity, other)? 2. Do instruments to screen for increased risk of suicide accurately identify adolescents, adults, and older adults who are at increased risk in primary care populations? Does the accuracy of the screening instruments vary by population characteristics? 3. Are there harms associated with screening for suicide risk in primary care settings? Do the harms vary by population characteristics? 4. For those identified as being at increased risk of suicide, do interventions to reduce suicide risk (behaviorally-based, including home visits or counseling for environmental change, or pharmacologic) result in improved health outcomes (decreased suicide attempts, decreased suicide deaths, improved functioning, improved quality of life, or improved health status)? Does the effect of the interventions vary by population characteristics? 5. For those identified as being at increased risk of suicide, do interventions to reduce suicide risk (behaviorally-based, including home visits or counseling for environmental change, or pharmacologic) result in improved intermediate outcomes (suicidal ideation, decreased access to means of suicide, increased treatment of previously undiagnosed mental health conditions, decreases in depressive symptomatology or hopelessness)? Does the effect of screening programs vary by population characteristics? 6. For those identified as being at increased risk of suicide, what are the harms of behaviorally-based or pharmacologic treatment to reduce suicide risk? Do the harms vary by population characteristics?