Islands are special places; they can be havens for unique plants and animals and refuges for wildlife. This book investigates the biogeography of butterfly species over the British islands, particularly the factors that influence their presence on the islands and that have made each island's butterfly fauna distinctive. The book contains a full log of records of species on the islands and much supporting information. The first three chapters set the scene, illustrating the basics of island biogeography theory, their changing circumstances during the current Holocene interglacial, and studies of natural history of British butterflies that mark the islands as the most intensively studied region for wildlife in the world. The book advances by increasing resolution downscale from a European continental perspective, through patterns and changes on the British mainland, a comparison of the two dominant islands of Britain and Ireland, to a close inspection of the dynamics of species on the multitude of offshore islands. Detailed investigations include contrasts in species' richness on the islands and then of the incidences of each species. Case studies highlight the continual turnover of species on islands. Attention is then given to evolutionary changes since the time that glaciers enveloped Europe. A powerful message is conveyed for the maintenance of butterfly species on the smaller British islands now experiencing population losses at a rate unprecedented since the spread of the last ice sheets: the incontrovertible importance of maintaining populations of species on nearby mainland sources for islands as pools for future migrants.