This reference and guide for those interested in modern infiltration theory presents the theoretical and mathematical basis of physically- based infiltration functions and tells how to apply theory to various hydrologic problems. It is assumed that the reader has an understanding of mathematics including basics of partial differential equations; however, mathematical complexities, especially lengthy derivations, are avoided when not needed. Emphasis is on one- dimensional, vertical infiltration such as for the rainfall-on-soil condition. Robust equations are supplied which can be applied in hydrologic models at a variety of scales for different objectives. Annotation copyrighted by Book News, Inc., Portland, OR.