What - Hybrid Diagnostic Modeling is the most recent development in diagnostic modeling. As a means of combining both Functional and Failure Mode models, Hybrid models the modeling reduction advantages of the functional modeling approach, while also providing a failure mode layer. Why - Hybrid Diagnostic Modeling is used for building models that endure throughout the entire development process by require the least amount of upkeep. Also used when conceptual designs must migrate into final designs with full traceability and validation support. Hybrid models that support both functions and failure modes are especially well suited to Prognostics development because of the way in which data is matured as part of creating predictive algorithms. When - When performed in the concept phase, Hybrid models typical are used mostly for their functional modeling. As the design progresses, failure modes appear as lower level models are built. The ability to simultaneously support both failure modes and functions allows the hybrid model to easily support mid-process analyse History - The Hybrid Diagnostic Model was officially created in 2002 in the product called eXpress. This product, a derivative of the original Dependency Modeling approach, was enhanced with a unique function and failure mode trade-off engine that provides its hybrid capabilities. Hybrid Diagnostics are seen as the wave of the future because of their ability to support the gamut of engineering activities. Currently, eXpress remains the only tool to support the hybrid diagnostic model.