This chapter provides a description of the procaryotic cell, focusing primarily on the bacterial cell. Archaea are discussed in more detail in chapter 20. Throughout this chapter, the term procaryote is used to mean both bacteria and archaea. The discussion begins with the general features of size, shape, and arrangement of procaryotic cells. Then the general features of biological membranes and the specific features of procaryotic membranes are given. Important internal structures of procaryotes, such as the cytoplasmic matrix, ribosomes, inclusion bodies, and the nucleoid are described, as well as structures external to the cell, such as the cell wall, glycocalyx, fimbriae, and flagella. The differences between the cell walls of gram-positive bacteria and gram-negative bacteria are discussed and the mechanism of this differential staining reaction is explained. The chapter concludes with a discussion of bacterial chemotaxis and bacterial endospores.