The book summarizes the achievements of the past decade in the biochemistry, bioenergetics, structural and molecular biology of respiratory processes in selected genera of the domain Bacteria along with an extensive coverage of the redox chains of extremophiles belonging to the Archaean domain. The volume is a unique piece of work since it contains a series of chapters dealing with metabolic features having important microbiological and ecological relevance such as the use of ammonium, iron, methane, sulfur and hydrogen as respiratory substrates or nitrous compounds in denitrification processes. Particular attention is also dedicated to peculiar groups of prokaryotes such as Gram positives, acetic acid bacteria, pathogens of the genera Helicobacter and Campylobacter, nitrogen fixing symbionts and free-living species, oxygenic phototrophs (Cyanobacteria) and anoxygenic (purple non-sulfur) phototrophs. The book is intended to be a long-term source of information for Ph.D. students, researchers and undergraduates from disciplines such as microbiology, biochemistry and ecology, studying basic and applied sciences, medicine and agriculture.