It is widely acknowledged that we have a duty to protect the environment. Yet, current environmental policy discussions demonstrate that fulfilling this in practice is a difficult, complex, and costly task. There are many ethical questions arising from such discussions. Should we care about the environment because it is economically valuable or because nature has intrinsic value? How do we establish an ethical trade-off between our current needs and those of future generations? Should we protect individual species or entire ecosystems instead? What way should we discuss societal values and ideals, or should scientific analysis take precedence within decision making practice? This book aims to tackle some of these thorny sustainability issues and responds to them with a cohesive, original alternative in the form of the precautionary ecosystem health principle (PEHP). It provides a detailed philosophical approach and advocates that a PEHP approach is able to overcome many of these stark and challenging difficulties within sustainability theory and environmental policy.