In order to grow and reproduce, cells need to assemble cell building blocks such as lipids, amino acids, and nucleic acids. This chapter delves into how microbes synthesize these required cell components. Autotrophic bacteria and archaea build themselves entirely from carbon dioxide and nitrogen gas plus a few salts. From these simple molecules, microbial enzymes construct proteins, the cell wall and envelope, and all the machinery of the cell. Some microbes produce complex secondary products with valuable properties, such as antibiotics. In the laboratory, microbial biosynthesis can be engineered to make cloned proteins, pesticides, and industrial reagents.