An ecosystem can be thought of a group of interdependent living organisms, along with that group's non-living surroundings, all of which is involved in a constant transfer of energy and mass within a general state of equilibrium or dis-equilibrium. Thermodynamics is the branch of physics that theorizes and models the flow and behavior of energy through any specific entity or system, and how that energy serves to "organize" or "disorganize" the system in question. Thus, one particularly important function served by thermodynamics is to quantify exactly how "organized" or "disorganized" a system is: something that is extremely useful to know when trying to understand how a dynamic ecosystem is behaving. Here for the first time in a book-length study, noted ecologist Sven Jorgensen has gathered together all the current thinking on how an ecosystem can be explained - and predicted - in terms of its thermodynamical behavior. Following introductory chapters on the fundamentals of the first, second, and third laws of thermodynamics, the book will then go on to explicate how thermodynamic theory can be specifically applied to the "measurement" of an ecosystem, including the assessment of an ecosystem's state of entropy and enthalpy. The book will even show economists how to put these theories to use when trying to quantify the movement of goods and services through another type of complex living system - a human society. This book will be of potential interest to a wide variety of professional and academic readers in all the various life science and environmental fields studying the behavior of complex living systems, including ecologists, biologists, environmental chemists, and even social scientists and applied mathematicians!