The enhanced definition of Mechatronics involves the four underlying characteristics of integrated, unified, unique, and systematic approaches. In this realm, Mechatronics is not limited to electro-mechanical systems, in the mul-ti-physics sense, but involves other physical domains such as fluid and thermal. This paper summarizes the mecha-tronic approach to modeling. Linear graphs facilitate the development of state-space models of mechatronic systems, through this approach. The use of linear graphs in mechatronic modeling is outlined and an illustrative example of sound system modeling is given. Both time-domain and frequency-domain approaches are presented for the use of linear graphs. A mechatronic model of a multi-physics system may be simplified by converting all the physical do-mains into an equivalent single-domain system that is entirely in the output domain of the system. This approach of converting (transforming) physical domains is presented. An illustrative example of a pressure-controlled hydraulic actuator system that operates a mechanical load is given.