The relevance of site characteristics, mainly population distribution, on the safety of NPPs was soon recognized. The ideas and concepts developed by the United States former Atomic Energy Commission (AEC) since 1962 have been maintained until now and have provided the basis for evaluating the site for NPPs; they also have shaped the design basis of the currently operating reactors. Because of the large impact of these considerations, it has been found of interest to present a short account of this historical development and the current situation regarding this matter.