The transport properties in two-phase (Ac, M) granular composites generally depend on several parameters: the interfaces (Ac/Ac, M/M, Ac/M), the grain sizes and morphologies, the percolation threshold. Generally in such (Ac, M) composites, one of the component (M) plays a mechanical role, and an other (Ac) presents a transport property as electron conduction, superconduction, or ionic conduction. We present here the various simulation approaches which can be used to better understand the final properties of such composites. Two types of composites can be considered: sintered two-phase composites in which chemical diffusions and interphase formation occur at the interfaces, polymer/ceramics composites in which weak links are involved between grains. To better understand the transport properties in two-phase composites three types of approaches are presented: (1) a microstructural approach; (2) the effective medium approximation; (3) the percolation theory. Several examples are selected to illustrate and discuss these various approaches.