[Clin Psychol Sci Prac 18: 126–141, 2011]
Advances in the scientific study and dissemination of evidence-based practices (EBPs) require psychometrically valid fidelity scales, which measure adherence to program models. We examined the literature on the Individual Placement and Support Fidelity Scale to illustrate the strengths and limitations of this methodology. We found that this scale had excellent psychometric properties. Nine of 10 studies assessing its predictive validity found positive associations with employment outcomes. Its use in quality improvement was supported by positive reports from seven multisite projects. Although not yet evaluated as an accreditation tool, three states have adopted the scale for reimbursement purposes. Development of valid fidelity scales is necessary for the field to advance. Technical and logistical challenges impede the replication of these findings for other EBPs.