Following the examination of carrier excitation and recombination in Chaps. 8 and 9 , respectively, this chapter develops the foundation for understanding a third important nonequilibrium process: carrier transport. Following the definition of electrical current and current density, carrier transport by drift and diffusion is discussed along with the concepts of carrier mobility, diffusion coefficient, scattering, and Einstein relation between mobility and diffusion coefficient. Ample examples illustrate these new concepts for real-world semiconductor materials and demonstrate problem-solving strategies related to carrier transport. Advanced topics include a detailed discussion of Hall effect measurements that are widely used to measure transport parameters such as the carrier type, concentration, and mobility, along with a unified picture of carrier transport within the context of the Boltzmann transport equation.