Synopsis The science dealing with the waters of the earth, their distribution on the surface and underground and the cycle involving evaporation, precipitation is known as 'hydrology'. The importance of this discipline was understood much earlier in our ancient civilization. The location of cities and important settlements along the rivers and near water bodies is the testimony of it. The lay out of settlements and building plans are with reference of the availability of their resources that may not be as scarce as we find it today. The association of history and civilization established the importance of rivers and other water bodies as the prime resource necessary for all forms of life on earth. According to the Markandya Purana all rivers are sacred, all flow towards sea. All are like mothers, all purge away sins. Indians consider their waters as sacred. It has been stated in ancient scriptures that the water of river Yamuna purify a man after a bath of seven days, those of Saraswati after a bath of three days, those of Ganges immediately on taking the bath; and those of Narmada on their mere sight. Regarding Tapi, it has been stated that mere remembering her purifies a man. The Hydrological Atlas of India is an attempt of the NATMO to transfer the knowledge so far collected by different concerned departments to the users and researchers, through a set of thematic maps showing hydrological setup of the country along with all the interrelated elements of geology, physiography, climate, soil, natural vegetation and land use. It provides an overview of the water potential of both the surface and ground water and their quantity, quality and availability. The map content provides logical links between physical and social environments. Each of the maps shows different aspects of water for a better understanding of natural environment, its interaction with the social and economic activities. Water, thus viewed is a highly valuable and mobile resource. The users of this Atlas are likely to be exposed to one of the great system of the nature, the hydrologic system of our country and its impacts on environment and human civilization. This Atlas should be useful to the governments, institutions and individuals who are working on water related issues. Further, it may provide some background information for possible interlinking of rivers in the country.