The book provides an overview of recent advances in the theoretical analysis of NPS pollution and regulation from an economic perspective. Besides specific policy recommendations, a common theme in the essays is the attempt to suggest regulatory approaches starting from the recognition of the problems of incomplete information encountered when dealing with NPS problems. Such problems, which can be traced back to the difficulty of identifying sources and measuring individual discharges, imply that, rather than monitoring emissions at source, alternative solutions have to be found to set regulatory policy instruments. In this sense, besides problems classified in the technical literature as NPS pollution, many of the considerations are also applicable to phenomena labelled as point-source problems, whenever -- despite the availability of technical means for measuring the volume and quality of emissions -- widespread and continuous monitoring of individual discharges is economically unfeasible, and alternative ways of establishing cause and effect links between economic activities and observed environmental quality impairments are required.