The introduction outlines the concept of the volume. It briefly sketches the state of research, it defines the key issues and it outlines the structures, dimensions and outreaches of the networks dealt with in the book. It reflects upon informal aspects of the networks, such as correspondences and exchanges between those scientists who played important parts in the global ecological networks and feature in many of the following chapters. It also refers to the institutional infrastructures which shaped the networks and are examined in the individual chapters, such as acclimatization societies, forest administrations, botanical and zoological gardens, natural history museums, agricultural colleges and colonial research stations. Following the results of actor-network-theory, the introduction defines three categories of agents of ecological change: firstly, European scientists and colonists, secondly, non-European actors, and thirdly, non-human agents of transfer, such as animals and plants. Furthermore, the introduction addresses the temporal dimensions of the networks. It problematizes their chronological organization and the role of different forms of temporality.