Some people are impatient with those who would review early efforts to determine the scope of the chemical hazardous waste problem in the United States. There are good reasons for their impatience: namely, the efforts reveal how little was known; the material is tedious; and it is not particu­ larly helpful for future planning. It might therefore be politic to skip quietly over initial efforts to estimate the scope of the problem. But there are two very strong counterarguments which led us to write this chapter. Uncer­ tainty and its impact on credibility and decisionmaking are major themes that run throughout this volume. To be consistent to this theme, the saga of efforts to find abandoned sites is presented. Second, as will be explained in this chapter, we are not sanguine about the final list of abandoned sites, the list of priority sites, nor about the absence of a comprehensive list of sites which would include active chemical sites, lagoons, and ponds on in­ dustrial properties and on military and mining sites.