The Nuclear Security Enterprise consists of the National Nuclear Security Administration (NNSA) plus a large, distributed system of laboratories, production plants, and other sites that are staffed by personnel working under management and operating contracts. In collaboration with the National Academy of Public Administration, Report 4 on Tracking and Assessing Governance and Management Reform in the Nuclear Security Enterprise evaluates the implementation plan developed by the National Nuclear Security Administration and Department of Energy in response to the FY2016 National Defense Authorization Act, and the subsequent implementation of such plan. The recommendations of this report will guide the NNSA as they reform management culture to a culture of performance, accountability, and credibility that is mission-driven.