This paper presents the systematic approach used for the independent verification and validation of a Joint-Modeling and Simulation System (J-MASS) threat system model. Verification is the process of determining that a model implementation accurately represents the developers conceptual description and specifications. To minimize cost and maximize benefit, the verification process should parallel the model development process. It should begin with initial model development and continues throughout the model development process. This approach results in early identification of problems. These can be resolved cost effectively as the model development progresses instead of at the end of model development where cost for changes can be significant. When performing the verification tasks, the verification team reports frequently tothe program office and the model developer to assure that any findings are available for immediate action, and that verification activities are in consonance with program needs. The verification process is divided into the following verificationtasks: software requirements verification, engineering design verification (top level), detailed design verification (software design), system test support, documentation verification, software verification, and verification reporting. The valithtion process determines the degree to which a model is an accurate representation of the real world phenomenon from the perspective of the intended use(s) ofthe model. The objective of the validation effort is to document the differences between the model and the actual system that may impact the intended use of the model. To accomplish a validation effort in a timely manner and at minimum cost, the validation process should be integrated into the model development and model verification processes. The validation process consists of the following tasks: determine the model user requirements, establish the validation data baseline, develop a validation test matrix, test the model, compare model parametric test data to the validation data baseline, compare model performance data to the baseline, determine any impacts to model use that result from differences, and develop the model validation report. This paper outlines the procedures used to accomplish verification and validation of J-MASS models.