An attempt is made to place before students (degree and post-degree) and professionals in the fields of Civil and Agricultural Engineerings, Geology and Earth Sciences, this important branch of Hydro science, i.e., Hydrology. It deals with all phases of the Hydrologic cycle and related topics in a lucid style and in SI system. There is a departure from empiricism, with emphasis on collection of hydrological data, processing and analysis of data and hydrological design on sound principles and matured judgement. Large number of hydrological design problems are worked out at the end of each article, to illustrate the principles involved and the design procedure. Problems for assignment are given at the end of each chapter, along with objective type and intelligence questions.