The study of the quality, movement, distribution, properties and characteristics of water present on Earth as well as other planets is known as hydrology. It also includes topics like environmental watershed management, water cycle and water resources management. The field has many sub-branches like ecohydrology, isotope hydrology, water quality, chemical hydrology, hydroinformatics, hydrogeology, drainage basin assessment, surface hydrology, hydrometeorology, etc. This textbook is a valuable compilation of topics, ranging from the basic to the most complex theories and principles in the field of hydrology. It will prove immensely beneficial to students involved in this area at various levels.