An investigation into landscape saturation has been carried out analytically using similarity parameters derived from topographic, soil, and climatic attributes. Three parameters (an input index (q/Z)(L/KS), convergence ratio (CR), and profile factor (B)) define the extent of hillslope saturation. From these, a single dimensionless parameter has been derived to describe the occurrence of saturation in planar, concave, and convex profile hillslope shapes, and with parallel, convergent, and divergent planforms. The relationship can be represented by a single dimensionless curve. The theory derived in this paper provides a basis for combining the individual parameters into a similarity criterion for saturation in landscapes. The theory and ensuing similarity hypothesis are applied to three natural catchments near Canberra, Australia, and are tested against observed rainfall-runoff data. The results support the validity of the similarity approach. There is a clear link between the distribution of hillslope similarity parameters and catchment saturation behavior.