The advances in both molecular biology and the physics of irreversible processes have offered hope for understanding living systems in terms of the known physical laws, and thus we shall be able to see life as one of the many phenomena displayed by the universe in its evolution. This book is an attempt to introduce physicists and physically-oriented students of the biological sciences to this view. An introductory discussion of the definition of "living" is followed by an overview of the properties of living systems as we know them. Then selected topics, chosen because of their fundamental importance to our understanding of living systems, are presented in greater detail. This book is therefore not a complete text of biophysical or biochemical topics. The subjects chosen for discussion are related to the origin of life, the physical requirements for ordered living systems, and the physical and chemical bases for the most fundamental phenomena displayed by living systems such as photosynthesis, energy transfer and storage, and reproduction. It is hoped that this will stimulate the interest and furnish the knowledge necessary to further explore these topics in the current literature.