Nataliya (Natasha) Shevchenko and Mary Popeck, both senior researchers in the CERT Division at Carnegie Mellon University's Software Engineering Institute, discuss the use of model-based systems engineering (MBSE), which, in contrast to document-centric engineering, puts models at the center of system design. MBSE is used to support the requirements, design, analysis, verification, and validation associated with the development of complex systems.