The role of non-native species in their new environments is one of the central issues in conservation biology and ecology today. This book presents a comprehensive evolutionary exploration of the complex and dynamic interactions between introduced species and native ones, and shows that non-native species can bring useful and important contributions to novel ecosystems. Based on a wide variety of examples and case studies, a strong case is made for a more positive and objective approach to non-native species and a greater appreciation of the valuable ecosystem services they provide.