In this <em>Very Short Introduction</em>, Terrence Allen and Graham Cowling offer an illuminating account of the nature of cells--their basic structure, forms, division, signaling, and programmed death. Allen and Cowling start with the simple "prokaryotic" cell--cells with no nucleus--and show how the bodies of more complex plants and animals consist of billions of "eukaryotic" cells, of varying kinds, adapted to fill different roles--red blood cells, muscle cells, branched neurons. The authors also show that each cell is an astonishingly complex chemical factory, the activities of which we have only begun to unravel in the past fifty years.