This treatise on Hydrology is an attempt to bridge the gap that exists between principles and practice in the subject. It lays importance on principles and concepts and simultaneously furnishes guidelines on practical use of the subject, through a large number of worked problems. The problems worked out are based mostly on field data. The book covers courses on Hydrology at both the U.G. and P.G. levels. It also provides reliable reference material to students preparing for competitive examinations such as GATE and IES. It further forms a ready reference guide to the practising engineers. The highlight and most distinguishing feature of the book is the way practically important topics on Frequency analysis, Regression analysis and Watershed modelling are dealt with. The book is expected to be of great help to the students at the U.G. level and as well to provide impetus to teachers to take up B.E. projects in this subject of great importance.