This chapter discusses in detail the process we used to engage stakeholders in further refining the scope of issues to consider in this environmental burden of disease assessment. First, we provide background on innate human cognitive biases that affect our perceptions of risk and how these biases pose challenges to rational priority setting. Then, we describe previous international experiences in prioritizing environmental risks to health for policymaking. Next, we describe the systematic approach used here to prioritize environmental risk factors—an approach that compensates for cognitive biases, incorporates scientific information, systematically involves multiple stakeholders, and builds on international experiences. Finally, we describe how we implemented this ranking process and how the results led to the eight environmental risk factor categories that are the subjects of the remaining chapters of this book: outdoor air pollution, indoor air pollution, occupational exposures, climate change, drinking water contamination, coastal water pollution, soil and groundwater contamination, and produce and seafood contamination.