Infiltration is a fundamental component of the hydrological cycle and its calculation is essential for the design of hydraulic works in irrigation engineering, hydrological and hydraulic engineering. For this reason, this book is to professionals in civil engineering, agronomic sciences and water sciences who need to estimate the infiltration rate in agricultural soils or perform water balance in small watersheds. It is also useful for newly graduated engineers or students interested in the subject. The author’s intention is to present several methods to estimate the speed of water infiltration in agricultural soils and small hydrological watersheds. This book is not a manual, however, each method is explained clearly and simply to facilitate its application in field, exposing the limitations and advantages of each one of them. The work that the reader has in his hands is practical and useful.