The intent of this guide is to provide both a summary of the basic concepts underlying the SCS hydro-logic methods and a guide to their use. Thus, this guide will fill a void thar currently exists. It is mainly concerned with the TR-20 method, which is a computer program, and the TR-55 methods, which includes a set of simplified procedures that are usually solved by hand. This guide has numerous features that should make it attractive to both the student or practicing engineer who want to learn the methods and those who need a well organized reference manual.