This textbook is the first of its kind to address the marine ecology of the entire pan-Arctic region. It offers an alternative to – and acts as a replacement for – earlier textbooks that took a more regional character, as well as it complements generic Arctic Ocean textbooks. To begin, the book investigates the Arctic Ocean in a global context. The initial chapters provide insights into processes that impact marine ecology, such as physical and chemical oceanography, river run-off, glacial melt, and sea ice dynamics. The book then systematically illuminates the various biotic players and processes in the Arctic Ocean, before ending with the effects of seasonality and ecotoxicology on biology. The effects and consequences of climate change are strongly marked throughout the book. The team of more than 70 authors originates from the entire community of nations that investigate the Arctic Ocean and adjacent seas. The main goal is to provide a joint textbook for marine ecology students that overcomes the regional approaches that have so far been the norm. Our endeavors focus upon understanding the entire expanse of the Arctic Ocean, not only its various sectors and subsystems. To comprehend the more or less circular Arctic Ocean, engirdled by vast landmasses of tundra, taiga, major rivers, and permafrost, it is important to educate a new generation of Arctic marine ecologists planning their regional investigations from a pan-Arctic perspective. Over time, this approach will support the indispensable, holistic understanding of the world’s smallest ocean, which is exposed to the greatest global warming and climate change.