Book excerpt: The diversity of species of plants and animals is the net result of the origin of new species by the splitting of existing lineages (speciation) and the loss of species through extinction. Why there are more species in some groups of organisms, in some places or at some times depends on the balance of these processes. This book explores the interaction between mechanisms and rates of speciation and these patterns of biological diversity, and is unusual in that it brings together the viewpoints of ecologists interested in the processes that generate patterns of diversity and evolutionary biologists who focus on mechanisms of speciation. It is intended to stimulate dialogue between these groups and so promote a more complete understanding of biological diversity.