Since July 2007, the Department of Energy (Department) and the National Nuclear Security Administration (NNSA) have required contractors to implement self-assessment systems to measure performance and help ensure effective and efficient mission accomplishment. In essence, contractors assessed and evaluated their own performance with some level of Federal oversight. Our audit found that despite at least 5 years of effort, NNSA and its support offices and site contractors had not yet implemented fully functional and effective contractor assurance systems. During recent Office of Inspector General (OIG) reviews, we identified significant implementation issues that adversely affected NNSA's ability to deploy an effective contractor governance system. For instance, contractor weaknesses identified at the site level were not effectively communicated to senior management officials and contractor self-assessments were not effective in identifying safety weaknesses subsequently identified by independent reviews. Further, we found that Federal officials had not provided effective oversight of contractor operations as part of the governance approach. To its credit, NNSA had self-identified deficiencies with contractor assurance system implementation and recognized the need to improve contractor assurance systems and its overall approach to contractor governance. NNSA plans an initiative to reform its contractor governance model. Therefore, we made several suggestions to NNSA to include establishing effective lines of communication between the sites and senior NNSA managers and mandating effective contractor self-assessments of operations. In response, NNSA management agreed with the suggestions and to address them in future efforts to re-evaluate and enhance their processes.