Chapter 2 provides a detailed account of the transport theories on continuum single-phase flows that include the laminar or turbulent flows of viscous fluids, the viscous fluid flows through porous media, and flows of granular particles. The most essential one is the continuum modeling of laminar flows of Newtonian fluids, which is the foundation of the Eulerian modeling approach of multiphase flows. The distinctly different transport mechanisms between a laminar flow and a turbulence flow as well as the flow regime transition conditions are presented. The essential aspects of the modeling of a turbulent flow of Newtonian fluid are also given. The basic theories of flows through porous media are represented by Darcy’s law, Ergun’s equation, and Brinkman's equation.The chapter also illustrates the continuum theory of granular flow, represented by the kinetic theory of granular flows whose transport mechanisms are dominated by inertia and interparticle collisions.