The first chapter is, in effect, a restatement of the Cell Theory in modern terms. The next chapters deal with the structure of macro-molecules and membranes, and the molecular architecture of cellular organelle. Then comes an account of bioenergetics and of energy transducers (such as chloraoplasts, contractile structures and ionic pumps). From this develops a detailed treatment of cell reproduction, cytodifferentiaon and cellular interaction. Finally the origin of cells during evolution is discussed. The book is aimed primarily at undergraduates with little knowledge of the subject but it should also be useful for graduates trying to keep up with recent advances.