The three National Nuclear Security Administration (NNSA) national security laboratories-Los Alamos National Laboratory (LANL), Lawrence Livermore National Laboratory (LLNL), and Sandia National Laboratories (SNL)-are a major component of the U.S. government's laboratory complex and of the national science and technology base. These laboratories are large, diverse, highly respected institutions with broad programs in basic sciences, applied sciences, technology development, and engineering; and they are home to world-class staff and facilities. Under a recent interagency agreement between the Department of Energy (DOE), Department of Defense, Department of Homeland Security, and the intelligence community, they are evolving to serve the needs of the broad national security community. Despite this broadening of substance and support, these laboratories remain the unique locus of science and engineering (S&E) for the U.S. nuclear weapons program, including, most significantly, the science-based stockpile stewardship program and the S&E basis for analyzing and understanding nuclear weapon developments of other nations and non-state actors. The National Research Council (NRC) was asked by Congress to assess the quality of S&E and the management of S&E at these three laboratories. The Quality of Science and Engineering at the NNSA National Security Laboratories is the second of two reports produced as part of this study. This report assesses the quality of S&E in terms of the capability of the laboratories to perform the necessary tasks to execute the laboratories' missions, both at present and in the future. The report identifies the following as four basic pillars of stockpile stewardship and non-proliferation analysis: (1) the weapons design; (2) systems engineering and understanding of the effects of aging on system performance; (3) weapons science base; and (4) modeling and simulation, which provides a capability to integrate theory, experimental data, and system design. The Quality of Science and Engineering at the NNSA National Security Laboratories offers a snapshot of the present with an eye to the future. This report discusses the current state of S&E and makes recommendations to maintain robust programs.