Modeling Challenges for CPS Systems Today’s complex cyber-physical systems require the use of a variety of models to capture different aspects of these systems: physical models, software models, control models, and so on. A critical challenge is to ensure consistency and completeness of these models. In this talk we describe an approach that uses architectural models as the basis for reconciliation. Specifically, a base architecture of the system is used as a unifying representation to compare the structure and semantics of the associated models through a set of architectural projections, or views. Each model is related to the base architecture through the abstraction of a corresponding architectural view, which captures structural and semantic correspondences between model elements and system entities. The use of the architectural view framework to relate system models from different domains is illustrated in the context of a quad-rotor air vehicle and an on-going collaboration with Toyota on future braking system design. Additionally we sketch some new ideas on the use of probabilistic modeling techniques for reasoning about human-in-the-loop CPS tasks, where the system must decide how, and to what extent, to involve users in achieving system goals.