Acknowledgements; Part I. Beyond Horses and Oak Trees: A New Theory of Individuation for Living Entities: 1. Introduction; 2. The meaning of 'a life'; 3. The poverty of examples; 4. Imaginary examples and conceptual analysis; 5. What is it?; Part II. The Biological and Philosophical Roots of Individuality: 6. Why biologists (should) care about individuality; 7. Philosophers on living entities; 8. Natural kinds and substantial kinds; 9. Patterns and natural kinds; Part III. Individuality and Equivocation: 10. Paradigm individuals: the higher animals; 11. Other possible solutions; 12. The proposed solution; Part IV. The Necessity of Biological Origin and Substantial Kinds: 13. A valid argument for sortal essentialism; 14. The necessity of biological origin; 15. Sex; 16. Species membership and the necessity of genealogy; Part V. Generation and Corruption: 17. Genetic individuals; 18. Functional individuals; 19. Developmental individuals; 20. Raising the dead; Part VI. Personal Identity Naturalized: Our Bodies, Our Selves: 21. Human beings as biological entities; 22. Is a person a human being?; 23. Conclusions; Appendix. Identity and sortals: why relative identity is self-contradictory; Notes; References; Index.