This chapter provides a description of the prokaryotic cell, including bacterial and archaeal cells. The discussion begins with the general features of size, shape, and arrangement of prokaryotic cells. Then the general features of biological membranes and the specific features of prokaryotic membranes are given. The cell wall is discussed with special reference to the differences between the cell walls of gram-positive bacteria and gram-negative bacteria, differential staining reactions, and the nature of S-layers.