Readers approaching this book should not expect a review of the diverse forms of parasitic organisms or a series of illustrations of the extraordinary adaptations parasitism has provided. This is a book of theory and graph, of generalization and synthesis. It is aimed at a broad audience, with the hope that the reader ‘when later gazing at a bird gliding overhead, will see not just the bird, but will also see (or at least imagine!) the flying assemblage of parasite species’.