Previously published in hardback and now made available in paperback, this ground-breaking book is a must for all interested in butterflies, whether as conservation biologist, amateur or professional entomologist or as a student studying the phenomenon of butterfly populations as part of a number of biology, ecology or conservation courses. Recently, many British butterflies have suffered severe declines whole others have flourished and expanded in range. This is the first book to describe the results from a British scheme to monitor butterflies during this period of change. The Monitoring Scheme, initiated in 1976 by the senior author is based on frequent counts at some 90 sites throughout Britain. The combined efforts of both amateurs and professionals have thus produced a dataset with no equivalent elsewhere in the world. The book therefore provides a unique perspective on trends in numbers, extinction and foundation of populations; flight periods, local distributions, migration and other aspects of population ecology. Practical problems encountered during the conservation of butterflies of individual sites are outlined. The relevance of this monitoring for an understanding of the effects of the weather - climatic warming - is described.