Models and simulations are SE tools used by multiple functional area disciplines during all life-cycle phases. Modeling is essential to aid in understanding complex systems and system interdependencies, and to communicate among team members and stakeholders. Simulation provides a means to explore concepts, system characteristics, and alternatives; open up the trade space; facilitate informed decisions and assess overall system performance. For additional information on the tools see DAG Chapter 4 section 4.3.19.1 [https://acc.dau.mil/dag4.3.19.1]. This sub-topical area contains information on the use of modeling and simulation in DoD acquisitions.