This new edition of a foundational text provides a contemporary review of cladistics, as applied to biological classification.

David M. Williams is a researcher at the Natural History Museum, London, specializing in diatom (Bacillariophyta) taxonomy and biogeography. He is the current president of the Systematics Association, London. He has written over 240 scientific papers and ten books.

Part I. The Interrelationships of Organisms: 1. What this book is about; 2. Classification; Part II. Systematics: Exposing Myths: 3. Relationship diagrams; 4. Essentialism and typology; 5. Monothetic and polythetic taxa; 6. Non-taxa or the absence of -phyly: paraphyly and aphyly; Part III. The Cladistic Programme: 7. Parameters of classification: ordo ab chao; Part IV. How to Study Classification: 8. Modern artificial methods and raw data; 9. How to study classification: consensus techniques and general classifications; 10. How to study classification - 'total evidence' vs 'consensus', character congruence vs taxonomic congruence, simultaneous analysis vs partitioned data; 11. How to study classification: natural methods I - consensus revisited; 12. How to study classification: natural methods II - beyond method, the philosophy of three-item analysis; Part V. Beyond Classification: 13. Beyond classification: how to study phylogeny; 14. The separation of classification and phylogenetics; 15. Further myths and misunderstandings.