Parasites evolve under selective pressures which are different from those acting on free-living organisms. This textbook presents these pressures and shows how they have shaped the ecology of parasites over evolutionary time. Broad theoretical concepts are explained simply and clearly and illustrated throughout with example organisms. The book should prove useful for advanced undergraduate biologists who are studying evolutionary biology, ecology, population biology, parasitology and evolutionary ecology. It should also be of interest to postgraduate students and researchers in the same fields.