This chapter provides information about the chemistry of the cell walls of bacteria and archaea. Bacteria have peptidoglycan, which contains NAG–NAM dimers with four amino acids making up the crossbridge. The specific configuration of these amino acids enables covalent bonds to unite the linear strands of the peptidoglycan into a single structure. The enzymology of this step-by-step assembly of the peptidoglycan is presented, and the points of inhibition by antibiotics are identified. The unique wall structures of acid-fast bacteria and endospores are presented. The structure, chemistry, function, and biosynthesis of S-layers at the surface of the bacterial cell are presented.