The discovery of how the machinery of life works, and how it is constructed, is one of the glories of 20th century science. By contrast, we know little of the origin and evolution of cells and their parts, and what we have learned is in dispute. This book surveys ongoing efforts to make cell evolution intelligible. The text revolves around a small set of fundamental questions: 1. How many kinds of cellular designs does our world hold, and how are they related? 2. Is the traditional metaphor of a tree of life still useful, or has it been superseded? 3. What are viruses, and how are they related to cells? 4 Can one construct a timeline for the origin and early history of life? 5. Do all living things share a common ancestor, and what was its nature? 6. Why are eukaryotic organisms so much more complex than prokaryotic ones, and how did they arise? 7. Has functional, adaptive organization increased over time, and if so, why? 8. Is there a way to generate functional organization that does not depend on heredity, and selection? 9. How did life emerge from the lifeless world of chemistry and physics? 10. Can a generalized theory of evolution explain the origin of life? 11. Is the history of life a succession of contingent events, or does it have direction and meaning?