The hydrologic cycle on land includes infiltration, runoff, and evapotranspiration. This chapter reviews the principles of infiltration and runoff and discusses parameterizations to scale runoff over large regions with heterogeneous soils. These parameterizations rely on statistical distributions to characterize soil moisture variability. A similar statistical approach accounts for nonlinearity in soil moisture effects on evapotranspiration using either continuous or discrete statistical distributions. Snow cover is particularly patchy, and models divide land into snow-covered and snow-free areas when calculating surface fluxes. Many models additionally account for heterogeneity in vegetation and soils by dividing a model grid cell into several tiles.