This book scrutinizes the growth of the ‘eco-terrorism’ movement operating on a global scale, focusing on the main groups and their more radical offshoots, both historically and those currently active. These include Earth First!, the Earth Liberation Front, the Animal Liberation Front and the Sea Shepherd Conservation Society. It critically examines how these groups form and how they have evolved, their key personnel, their strategies and tactics, principles, motivating philosophies and attitudes to violence. Specifically, the book seeks to understand whether such groups inevitably evolve from activists to militants to terrorists, as the literature suggests. Lastly, it considers the future of such groups, asking whether they will become more prominent as more people become ecologically aware and as global environmental conditions deteriorate, or whether such groups have peaked as a force for environmental change.