This textbook examines the fundamental principles of microbial metabolism and how a microbe's ecology is intrinsically interwoven with and a consequence of its metabolism. Further, it answers many questions frequently asked by students, such as: What are the mechanistic connections between simple phenotypic traits, ecological patterns and microbial metabolism and diversity? In the process, readers will be introduced to essential topics like metabolism and metabolic pathways, flux of energy and nutrients, genome size and fitness, competition, selection and drift. Moreover, the book conveys fundamental principles that show students how to approach the field of microbiology from a different, more unifying angle, e.g., how microbes’ access to environmentally available energy resources and the specific metabolism involved lies at the root of every ecologically significant microbial speciation. This aspect, together with its special focus on metabolism and ecological implications, make the book a must-read for all students of microbiology. This textbook examines the fundamental principles of microbial metabolism and how a microbe's ecology is intrinsically interwoven with and a consequence of its metabolism. Further, it answers many questions frequently asked by students, such as: What are the mechanistic connections between simple phenotypic traits, ecological patterns and microbial metabolism and diversity? In the process, readers will be introduced to essential topics like metabolism and metabolic pathways, flux of energy and nutrients, genome size and fitness, competition, selection and drift. Moreover, the book conveys fundamental principles that show students how to approach the field of microbiology from a different, more unifying angle, e.g., how microbes’ access to environmentally available energy resources and the specific metabolism involved lies at the root of every ecologically significant microbial speciation. This aspect, together with its special focus on metabolism and ecological implications, make the book a must-read for all students of microbiology. Alfred M. Spormann is a microbial physiologist and biochemist, and a Professor at Stanford University. Since his PhD studies with Rolf Thauer, he has been researching microbial metabolism of diverse anaerobic microbes. He joined the faculty at Stanford University in 1994 after postdoctoral work with Harry P. C. Hogenkamp and A. Dale Kaiser, Stanford University. He has been teaching courses in Microbiology, Environmental Microbiology, and Microbial Metabolism for the last 30 years as well as the Woods Hole Microbial Diversity Course for 4 years, and the Hopkins Microbiology Course for 12 years.