The present book entitled “Hydrogeochemistry in Chhoti Gandak River basin, Ganga plain” comprises hydrogeochemical studies of Chhoti Gandak River, a tributary of Ghaghara River in Uttar Pradesh state of India. This book is basically a part of research works carried out during the Ph.D. of Dr. Vikram Bhardwaj from Centre of Advanced Study in Geology, University of Lucknow, India. This book has several basic and logical conclusions regarding the Hydrogeochemistry of Chhoti Gandak River basin, also including the major ion chemistry during the different existing seasons (pre-monsoon, monsoon, and post-monsoon) in the region. This book also discusses about the Sources and mechanisms controlling major ion chemistry, Seasonal variation of solutes, Water mineral equilibrium and major Hydrochemical facies of the basin. It also has comparison with other Indian and World rivers. This book may help to evolve the methodology for detailed seasonal hydrogeochemical investigations for similar basins and will be of immensely use for the students, teachers and researchers of this field and it can be used as a standard reference book.