Abstract: The Veterans Health Administration (VHA) has rolled out evidence-based psychotherapies (EBPs) for posttraumatic stress disorder (PTSD); however, reach has remained low, and there is a need for briefer interventions. The National Center for PTSD conducted a facilitated learning collaborative to train clinicians and support VHA PTSD teams in their adoption of an emerging best practice, written exposure therapy (WET). Guided by the Reach, Effectiveness, Adoption, Implementation, and Maintenance (RE-AIM) evaluation framework, the present study utilized longitudinal data from 178 clinicians and 556 patients across seven training cohorts to evaluate key clinical and implementation outcomes and whether clinic (i.e., implementation climate) or clinician factors (i.e., treatment attitudes) were associated with effectiveness and implementation. Intent-to-treat analyses indicated WET was effective in reducing PTSD (d = 0.54) and depression symptoms (d = 0.39). Data indicated that 87.60% of clinicians reported using WET 6 months postconsultation. Clinic-wide reach was modest after training (14.53% of individuals with PTSD); however, WET-trained clinicians continued to offer WET to an average of 87.38% of their patients. Fidelity remained high after training, with essential session elements most often being offered 'always' (M = 6.65 on a scale from 1 to 7). More positive postconsultation clinician treatment attitudes predicted higher posttraining rates of having patients engaged in WET. Clinician treatment attitudes and implementation climate did not predict any other implementation or effectiveness outcomes examined. Results suggest that WET implementation is advancing in VHA, with good clinical outcomes. Data provide evidence that a facilitated learning collaborative can be used to support and scale EBPs.