Suicide has been an increasingly prominent health concern among Veterans over the past 20 years. The Department of Veterans Affairs (VA) National Strategy for Preventing Veteran Suicide calls for robust and innovative solutions to existing suicide prevention efforts, including improvements to existing psychotherapeutic interventions. Effective suicide prevention interventions should identify and target mechanisms of suicide risk in the most efficient manner possible. One strategy includes a skills-based approach to reducing psychological inflexibility (cf. distress) related to suicidal ideation, thereby preventing suicidal thoughts from progressing to more severe forms of self-directed violence. Moreover, distilling these treatment components into a format that is more easily disseminated (i.e., single session, web-based) would improve Veteran access to effective suicide prevention interventions. Unfortunately, few clinical suicide prevention interventions have adopted either of these approaches, and none to date appear to have combined them in a manner that would provide an effective adjunctive suicide-specific intervention that could be administered across both traditional and non-traditional (e.g., primary care, emergency clinics) mental health settings. To that end, the Principal Investigator (PI) previously developed and tested a web-based intervention designed to reduce psychological inflexibility related to suicidal ideation, termed Re-Evaluating Suicidal Thoughts (REST). In a randomized clinical trial (RCT) of 98 non-Veteran outpatients, REST reduced psychological inflexibility and severity of suicidal ideation compared to controls. In a one-arm acceptability trial of 24 Veteran outpatients, REST was rated as highly relevant, helpful, and easy to use. The objective of the current proposal is therefore to evaluate the effectiveness of REST as an adjunctive suicide prevention intervention among Veterans in an integrated health care setting. The specific aims are to: evaluate the effect of REST on psychological inflexibility of suicidal ideation (Aim 1); evaluate the effect of REST on suicidal ideation severity and self-directed violence (Aim 2); and identify the therapeutic mechanism of REST in reducing suicidal ideation severity (Aim 3). Primary hypotheses include: compared to controls, REST will result in lower psychological inflexibility of suicidal ideation at one-week follow-up (Hypothesis 1) and lower suicidal ideation severity and reported self-directed violence at one-month follow-up (Hypothesis 2a and b); and that reductions in psychological inflexibility will account for reductions in suicidal ideation severity and self- directed violence (Hypothesis 3a and b). To accomplish these aims, the PI will recruit Veterans with current suicidal ideation (N = 150) to be randomized to receive REST or maintain treatment-as-usual (TAU control). Self- report measures of psychological inflexibility and severity of suicidal ideation will be admi...