The scientific study of organisms in the sea is referred to as marine biology. It classifies the species on the basis of the environment rather than on taxonomy. There are various habitats which are studied in marine biology such as kelp forests, coral reefs, thermal vents, seagrass meadows and tidepools. There are a wide range of organisms that are studied in marine biology, from zooplankton and phytoplankton to cetaceans. There are many sub-fields of marine biology. A few of them are ichthyology, phycology, invertebrate zoology, etc. Marine biology also studies the physical effects of continual immersion in sea water, adaptation to a salty environment, as well as the effects of various changing oceanic properties on marine life. This textbook attempts to understand the multiple branches that fall under the discipline of marine biology and how such concepts have practical applications. It aims to equip students and experts with the advanced topics and upcoming concepts in this area. This book is an essential guide for both academicians and those who wish to pursue this discipline further.