This chapter discusses the consequences of our economic activities, giving consideration to the wastes that are emitted by our industrial systems. Until comparatively recently in history, there was little concern expressed about industrial effluents and it was generally considered that the environment could be used as an infinitely large sink into which wastes could be deposited without there being any lasting consequences. This view is clearly incorrect. All human activity has an impact on the environment, some things more than others. But how do we know how much harm a particular activity is causing and how can we compare one activity with another or find ways to reduce environmental impact?