The new series "Microbiology Monographs" begins with two volumes on intracellular components in prokaryotes. In this second volume, "Complex Intracellular Structures in Prokaryotes," the components, labelled complex intracellular structures, encompass a multitude of important cellular functions. Continuing and newly initiated research will provide a clearer understanding of the complex intracellular structures known at present and will bring to light surprising new ones as well. "Complex Intracellular Structures in Prokaryotes" provides historical background and comprehensive reviews of ten topics that cover the spectrum of the complex intracellular structures of prokaryotes: proteasomes, phycobilisomes, chlorosomes, gas vesicles, carboxysomes, magnetosomes, intracytoplasmic membranes, membrane-bound nucleoids, anammoxosomes, and cytoarchitecture of Epulopiscium spp. Cameos of selected additional structures are presented to broaden the scope of the volume and to generate increased interest in these structures.