This book presents opposing views on the current philosophical and conceptual issues of the Species Problem in biology. Topics include ontology of species, definitions of species category and units, species rank, speciation issues, nomenclature, ecology, and species conservation.

Section 1. Concepts and theories 1. We Are Nearly Ready to Begin the Species Problem 2. Is the Species Problem That Important? 3. 'Species' as a technical term: Multiple meanings in practice, one idea in theory 4. What Should Species Be? Taxonomic Inflation and the Ethics of Splitting and Lumping 5. The Good Species Section 2. Practice and methods 6. Species in the Time of Big Data: The Multi-species Coalescent, the General Lineage Concept, and Species Delimitation 7. Species delimitation using molecular data 8. Taxonomic order, disorder and governance Section 3. Ranks and trees and names 9. Ecology, evolution, and systematics in a post-species world 10. The species before and after Linnaeus - tension between disciplinary nomadism and conservative nomenclature 11. Taxonomic hierarchies as a tool for coping with the complexity of biodiversity Section 4. Metaphysics and epistemologies 12. The species problem from a conceptualist's viewpoint 13. (Some) Species are Processes 14. Metaphysical presuppositions about species stability: problematic and unavoidable 15. Critique of taxonomic reason(ing): nature's joints in light of an 'Honest' Species Concept and Kurt Hubner's historistic philosophy of science Afterword 16. Continuing After Species: An Afterword