The new series “Microbiology Monographs” begins with two volumes on intracellular components in prokaryotes. In this first volume, “Inclusions in Prokaryotes”, the components, labeled inclusions, are defined as discrete bodies resulting from synthesis of a metabolic product. Research on the biosynthesis and reutilization of the accumulated materials is still in progress, and interest in the inclusions is growing. This comprehensive volume provides historical background and comprehensive reviews of eight well-known prokaryotic inclusions.