We present you with an updated reference book aimed for upper-level undergraduate and graduate students interested in Marine Biology. The textbook is designed to introduce the fundamentals of marine organisms and their ecological roles in the world's oceans, and is organized by functional groups emphasizing marine biodiversity rather than systematics or habitats. Each chapter has been written and peer-reviewed by renowned international experts in their respective fields, and includes updated information on relevant topics, from the microbial loop and primary production in the oceans, to marine megafauna and the impacts of projected climate change on marine life and ecosystems.