This book is intended to introduce the science of ecosystem ecology to advanced undergraduate students, beginning graduate students, and practicing scientists from a wide array of disciplines. We also provide access to some of the rapidly expanding literature in the many disciplines that contribute to ecosystem understanding. The first part of the book provides the context or understanding ecosystem ecology. We introduce the science of ecosystem ecology and place it in the context of other components of the Earth System - the atmosphere, ocean, climate and geological systems. We show how these components affect ecosystem processes and contribute to the global variation in terrestrial ecosystem structure and processes. In the second part of the book, we consider the mechanisms by which terrestrial ecosystems function and focus on the flow of water and energy and the cycling of carbon and nutrients. We then compare and contrast these cycles between terrestrial and aquatic ecosystems. We also consider the important role that organisms have on ecosystem processes through trophic interactions (feeding relationships), environmental effects, and disturbance. The third part of the book addresses temporal and spatial patterns in ecosystem processes. We finish by considering the integrated effects of these processes at the global scale and their consequences for sustainable use by human societies. Powerpoint lecture notes developed by one of the authors are available online (www. faculty.uaf.edu/fffsc/) as supplementary material.