A method for the evaluation of military hybrid electric vehicle thermal management systems has been developed. The approach allows for the generation of a set of evaluation metrics for determination of the effectiveness of existing systems and the means to assess alternative concepts and advanced approaches. Further, through the use of a set of deterministic performance metrics the methodology allows for evaluation of performance margins for adverse boundary conditions and system operations. The thermal management systems of military hybrid electric vehicles can face challenging performance goals under the burden of unfavorable operating conditions. The cooling requirements of engines, motors, and power electronics impose specific requirements on thermal management system performance in terms of threshold temperatures and heat rejection capability. In addition, vehicle packaging concerns impose restrictions in terms of both volumetric occupancy and system weight. Acknowledgement of these concerns has led to thermal management system evaluation metrics in two separate classes: performance-based metrics and packaging-based metrics. Performance-based metrics allow for a means to determine whether a vehicle thermal management system can meet maximum thermal demands at the worst case boundary conditions. Further, this methodology establishes a design metric for quantifying thermal management system hotel loads. Performance metrics allow for a structured approach to identify system over-design and/or functional margin deficiencies under a worst-case operational scenario. This approach can be used for the evaluation of existing vehicle systems through operational data and conceptual designs through analytical performance predictions. The proposed methodology allows for the comparison of systems both within and across classes of vehicles. Further, this approach allows for the evaluation of system design maturity, identify potential areas of improvement and quantify significant technological advancements.